Specifically Designed Constructed Wetlands: A Novel Treatment 

Approach for Scrubber Wastewater 

 

Scientific Final Report 

September 1, 2004—September 1, 2005 

Prepared by: 

John H. Rodgers, Jr., Ph.D., Professor, Clemson University 

James W. Castle, Ph.D., Assoc. Professor, Clemson University 

Chris Arrington, Graduate Research Assistant, Clemson University 

Derek Eggert, Graduate Research Assistant, Clemson University 

Meg Iannacone, Graduate Research Assistant, Clemson University 

September 2005 

United States Department of Energy 

Award # DE-FG26-04NT42178 

Clemson University 

300 Brackett Hall 

Clemson, SC 29634 
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Disclaimer 

“This report was prepared as an account of work sponsored by an agency of the United States 

Government. Neither the United States Government nor any agency thereof, nor any of their 

employees, makes any warranty, express or implied, or assumes any legal liability or 

responsibility for the accuracy, completeness, or usefulness of any information, apparatus, 

product, or process disclosed, or represents that its use would not infringe privately owned rights. 

Reference herein to any specific commercial product, process, or service by trade name, 

trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, 

recommendation, or favoring by the United States Government or any agency thereof. The 

views and opinions of authors expressed herein do not necessarily state or reflect those of the 

United States Government or any agency thereof.” 
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Foreword 

This scientific progress report is organized by the three research objectives or tasks: 

Task 1: 

To measure performance of a pilot-scale constructed wetland treatment system in terms of 

decreases in targeted constituents (Hg, Se and As) in FGD wastewater. 

Task 2: 

To determine how the observed performance is achieved (both reactions and rates) through 

sequential extractions of these elements from sediments. 

Task 3: 

To measure performance in terms of decreased bioavailability of these elements (i.e. toxicity of 

sediments in constructed wetlands and toxicity of outflow waters from the treatment system). 

Within the report, each section is divided and classified as TASK 1, 2, and 3. Discussions and 

conclusions are included in each section, along with an overall conclusion from data collected 

during the full year of funding. 

 
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Abstract 

A pilot-scale wetland treatment system was specifically designed and constructed at Clemson 

University to evaluate removal of mercury, selenium, and other constituents from flue gas 

desulfurization (FGD) wastewater. Specific objectives of this research were: (1) to measure 

performance of a pilot-scale constructed wetland treatment system in terms of decreases in 

targeted constituents (Hg, Se and As) in the FGD wastewater from inflow to outflow; (2) to 

determine how the observed performance is achieved (both reactions and rates); and (3) to 

measure performance in terms of decreased bioavailability of these elements (i.e. toxicity of 

sediments in constructed wetlands and toxicity of outflow waters from the treatment system). 

Performance of the pilot-scale constructed wetland treatment systems was assessed using two 

criteria: anticipated NPDES permit levels and toxicity evaluations using two sentinel toxicitytesting organisms (Ceriodaphnia dubia and Pimephales promelas). These systems performed 

efficiently with varied inflow simulations of FGD wastewaters removing As, Hg, and Se 

concentrations below NPDES permit levels and reducing the toxicity of simulated FGD 

wastewater after treatment with the constructed wetland treatment systems. Sequential extraction 

procedures indicated that these elements (As, Hg, and Se) were bound to residual phases within 

sediments of these systems, which should limit their bioavailability to aquatic biota. 

Sediments collected from constructed wetland treatment systems were tested to observe toxicity 

to Hyalella azteca or Chironomus tetans. Complete survival (100%) was observed for H. azteca 

in all cells of the constructed wetland treatment system and C. tentans had an average of 91% 

survival over the three treatment cells containing sediments. Survival and growth of H. azteca

and C. tentans did not differ significantly between sediments from the constructed wetland 

treatment system and controls. Since the sediments of the constructed wetland treatment system 

are repositories for As, Hg, and Se and the bioavailability of these elements decreased after 

deposition, the pilot-scale constructed wetland treatment system contributed significantly to 

mitigation of risks to aquatic life from these elements. 
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Executive Summary 

A pilot-scale wetland treatment system was specifically designed and constructed at Clemson 

University to evaluate removal of mercury, selenium, and other constituents from flue gas 

desulfurization (FGD) wastewater. Specific objectives of this research were: (1) to measure 

performance of the pilot-scale constructed wetland treatment system in terms of decreases in 

targeted constituents (Hg, Se and As) in the FGD wastewater; (2) to determine how the observed 

performance is achieved (both reactions and rates); and (3) to measure performance in terms of 

decreased bioavailability of these elements (i.e. toxicity of sediments in constructed wetlands and 

toxicity of outflow waters from the treatment system). This Scientific Final Progress Report 

provides a description of the configuration and current design characteristics of the pilot 

constructed wetland treatment system and performance results. Initial evaluations of 

performance contained in this progress report involved FGD wastewaters formulated based upon 

analyses of several actual FGD waters. 

Performance of the pilot constructed wetland treatment systems at this final stage indicates that 

the system is decreasing aqueous concentrations of the targeted wastewater constituents (As, Hg, 

and Se) for the majority of the wastewaters. The removal rates of mercury were consistently 

greater than 90% for three of simulated FGD wastewaters tested and ranged from 64% to 97% 

for all FGD wastewaters except for the high ionic strength FGD wastewater (week 7), in which 

the concentration of mercury was already below the predicted NPDES permit level of 0.001 

mg/L. Selenium removal rates were relatively stable throughout this study with a range of 84 to 

90% removal by the pilot-scale constructed wetland treatment systems. Arsenic removal, 

however, varied throughout the study with higher removal rates occurring during the high ionic 

strength FGD wastewaters (~70%). Removal rates of arsenic in these simulated FGD 

wastewaters are of lesser importance than Hg or Se, since the actual FGD wastewaters that we 

have analyzed to date had lower concentrations of arsenic than the specified NPDES limits. 

Sequential extraction procedures were used to quantitatively measure the immobilization of these 

elements of concern in the sedimentary component of these systems. Data gathered by this 

procedure indicate that most of As, Hg, and Se is bound to residue phases within the sediment, 

and the dissolution or re-solubility of these elements is unlikely to occur under environmental 

conditions within this treatment system (not thermodynamically favored). In toxicity 

experiments, we observed a significant increase in survival, growth, and reproduction for 

organisms exposed to samples of the final outflow versus inflow simulated FGD wastewater. 

Chloride concentrations are an important factor in this treatment process and satisfactory 

chloride levels (~4000mg/L) were achieved in these experiments by dilution with moderately 

hard water. 

Components of the system were manipulated to enhance removal of these targeted constituents 

and the contributions of these changes to transfers and transformations of As, Se, and Hg were 

assessed. Toxicity evaluations were conducted to relate these system component changes to 

bioavailability of these elements to the sentinel species used in NPDES toxicity tests. Bulk 

sediment toxicity was evaluated using both H. azteca and C. tentans . Since the sediments of the 

constructed wetland treatment system are repositories for As, Hg, and Se and the bioavailability 

of these elements decreased after deposition, the pilot-scale constructed wetland treatment 

system contributed significantly to mitigation of risks to aquatic life from these elements. 
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Table of Contents 

ABSTRACT................................................................................................................................... 3 

EXECUTIVE SUMMARY..................................................................................4 

TASK ONE ...........................................................................................................................9-48 

INTRODUCTION........................................................................................................................ 9 

MATERIALS AND METHODS ............................................................................................... 10 

System Configuration ................................................................................................................... 10 

Actual FGD Wastewater............................................................................................................... 11 

Simulated FGD Wastewater ......................................................................................................... 11 

Analytical Methods....................................................................................................................... 13 

Evaluation of Wetland Plants........................................................................................................ 14 

RESULTS ..................................................................................................................................... 14 

Primary Targeted Constituents ..................................................................................................... 14 

Other Constituents of Interest ....................................................................................................... 17 

DISCUSSION .............................................................................................................................. 46 

CONCLUSIONS ......................................................................................................................... 47 

REFERENCES............................................................................................................................ 48 

TASK TWO ...................................................................................................................... 49-55 

INTRODUCTION....................................................................................................................... 49 

MATERIALS AND METHODS ............................................................................................... 48 

Sequential Extraction Procedures..........................................................................49 

RESULTS .................................................................................................................................... 51 

DISCUSSION .............................................................................................................................. 54 

CONCLUSIONS ......................................................................................................................... 54 

REFERENCES............................................................................................................................ 55 

TASK THREE ...................................................................................................................56-69 

INTRODUCTION....................................................................................................................... 56 

MATERIALS AND METHODS ............................................................................................... 57 

Toxicity Experiments.........................................................................................57 

RESULTS .................................................................................................................................... 60 

DISCUSSION .............................................................................................................................. 69 

CONCLUSIONS ......................................................................................................................... 70 

OVERALL CONCLUSIONS..............................................................................71 

REFERENCES............................................................................................................................ 72 
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List of Tables 

Table 1. Acclimation FGD wastewater loaded into the pilot-scale constructed wetland 

 treatment system (listed as weeks 1-4). 

Table 2. Classification and targeted concentrations of elements of interest in four simulated FGD 

wastewaters used throughout this phase one DOE study.

Table 3. Targeted constituents and sources for simulated FGD wastewater. 

Table 4. Analytical methods for parameters monitored weekly from the FGD pilot constructed 

wetland systems. 

Table 5. Simulated FGD wastewater physical and chemical properties analyzed in a pilot 

constructed wetland system. 

Table 6. Monthly hydrosoil oxidation-reduction (redox) potential in the FGD pilot-scale 

constructed wetland systems. 

Table 7. Summary of sequential extraction procedures for Hg (modified from Lechler et al. 

 1997). 

Table 8. Summary of sequential extraction method for Se (modified from Chao and Sanzolone 

 1989). 

Table 9. Summary of sequential extraction procedure for As (modified from Wenzel et al. 2001 

 and Schank 2003). 

Table 10. Summary of sediment characteristics. 

Table 11. Elements and form used for amendments of simulated FGD wastewater. 

Table 12. Analytical methods for parameters monitored for FGD wastewater. 

Table 13. Measurements of parameters from inflow to outflow of the constructed wetland 

 treatment systems. 

Table 14. Sediment toxicity results in terms of survival and growth measurements of Hyalella 

 azteca for wetland treatments and controls. 

Table 15. Sediment toxicity results in terms of survival and growth measurements of 

 Chironomus tentans for wetland treatments and controls. 

List of Figures 

Figure 1. Schematic of the pilot constructed wetland system for evaluating treatment of FGD 

wastewater. 

Figure 2. Pilot constructed wetland system at Clemson University for treating FGD wastewater. 

Figure 3. Total mercury in simulated FGD wastewater treated by a pilot constructed wetland 

 system during the acclimation period (Weeks 1 to 4). 

Figure 4. Average total mercury in simulated FGD wastewater treated by a pilot constructed 

 wetland system for the high ionic strength FGD wastewater (Weeks 9 and 10). 

Figure 5. Average total mercury in simulated FGD wastewater treated by a pilot constructed 

 wetland system for the high-intermediate ionic strength FGD wastewater (Weeks 11 to 

 20). 

Figure 6. Total mercury in simulated FGD wastewater treated by a pilot constructed wetland 

 system for the first week of low-intermediate ionic strength FGD wastewater (Week 

 23). 
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Figure 7. Total mercury in simulated FGD wastewater treated by a pilot constructed wetland 

 system for the second week of low-intermediate ionic strength FGD wastewater 

 (Week 24). 

Figure 8. Total selenium in simulated FGD wastewater treated by a pilot constructed wetland 

 system during the acclimation period (Weeks 1 to 4). 

Figure 9. Average total selenium in simulated FGD wastewater treated by a pilot constructed 

 wetland system for the high ionic strength FGD wastewater (Weeks 9 and 10). 

Figure 10. Average total selenium in simulated FGD wastewater treated by a pilot constructed 

 wetland system for the high-intermediate ionic strength FGD wastewater (Weeks 11 

 to 20). 

Figure 11. Total selenium in simulated FGD wastewater treated by a pilot constructed wetland 

 system for the first week of low-intermediate ionic strength FGD wastewater (Week 

 23). 

Figure 12. Total selenium in simulated FGD wastewater treated by a pilot constructed wetland 

 system for the second week of low-intermediate ionic strength FGD wastewater 

 (Week 24). 

Figure 13. Average total arsenic in simulated FGD wastewater treated by a pilot constructed 

 wetland system for the high ionic strength FGD wastewater (Weeks 9 and 10). 

Figure 14. Average total arsenic in simulated FGD wastewater treated by a pilot constructed 

wetland system for the high-intermediate ionic strength FGD wastewater (Weeks 11 

to 20). 

Figure 15. Total arsenic in simulated FGD wastewater treated by a pilot constructed wetland 

system for the first week of low-intermediate ionic strength FGD wastewater (Week 

23). 

Figure 16. Total arsenic in simulated FGD wastewater treated by a pilot constructed wetland 

 system for the second week of low-intermediate ionic strength FGD wastewater 

 (Week 24). 

Figure 17. Hydrosoil oxidation-reduction (redox) potential for Train A of the FGD pilot-scale 

constructed wetland system. 

Figure 18. Hydrosoil oxidation-reduction (redox) potential for Train B of the FGD pilot-scale 

constructed wetland system. 

Figure 19. Hydrosoil oxidation-reduction (redox) potential for Train C of the FGD pilot-scale 

constructed wetland system. 

Figure 20. Sequential extraction of Hg (A), Se (B), and As (C) in sediment collected from the 

 first, second, and fourth planted wetland cells. 

Figure 21. Response, in terms of survival, of C. dubia to the inflow and the outflow from the 

 treatment system for Sample One simulated FGD wastewater (Trains A, B, and C 

 combined). Concentrations of 0.39% post-treatment and 50% pre-treatment were not 

 tested 

Figure 22. Response, in terms of survival, of C. dubia to the inflow and the outflow from the 

 treatment system for Sample Two simulated FGD wastewater (Trains A, B, and C 

 combined). Concentrations of 0.39% post-treatment and 50% pre-treatment were not 

 tested. 

Figure 23. Response, in terms of survival, of P. promelas to the inflow and the outflow from the 

 treatment system for Sample One simulated FGD wastewater (Trains A, B, and C 
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 combined). Concentrations of 0.39% post-treatment and 50% pre-treatment were not 

 tested. 

Figure 24. Response, in terms of survival, of P. promelas to the inflow and the outflow from the 

treatment system for Sample Two simulated FGD wastewater (Trains A, B, and C 

combined). 

Figure 25. Response, in terms of reproduction, of C. dubia to the inflow and the outflow from the 

treatment system for Sample One simulated FGD wastewater (Trains A, B, and C 

combined). Concentrations of 0.39% post-treatment and 50% pre-treatment were not 

tested. 

Figure 26. Response, in terms of reproduction, of C. dubia to the inflow and the outflow from the 

treatment system for Sample Two simulated FGD wastewater (Trains A, B, and C 

combined). Concentrations of 0.39% post-treatment and 50% pre-treatment were not 

tested. 

Figure 27. Comparative responses, in terms of survival, of C. dubia and P. promelas to simulated 

 FGD wastewater Sample One. 

Figure 28. Comparative responses, in terms of survival, of C. dubia and P. promelas to simulated 

FGD wastewater Sample Two. Concentrations of 0.39%, 0.78%, 1.56%, and 3.125% 

for P. promelas and 37.5%, 50%, 62.5%, and 75% for C. dubia were not tested. 

Figure 29. Comparative responses, in terms of survival, of C. dubia to simulated FGD 

wastewater Samples One and Two. 

Figure 30. Comparative responses, in terms of survival, of P. promelas to simulated FGD 

wastewater samples one and two. Concentrations of 0.39%, 0.78%, 1.56%, and 

3.125% for Sample Two and 37.5%, 50%, 62.5%, and 75% for Sample One 

were not tested. 

 
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Scientific Final Report 

TASK 1 

Introduction 

The purpose of this document is to report progress on this study conducted to evaluate the 

efficacy of specifically designed constructed wetland systems for treatment of flue gas 

desulfurization (FGD) wastewater, reactions and rates (for Hg, Se, and As), and toxicity of 

discharged wastewater from these systems. In order to efficiently implement FGD units at 

fossil-fueled power plants, an effective and reliable wastewater treatment system is needed. 

Large volumes of wastewater will be produced at each site from the FGD process, and that water 

must be treated to eliminate contaminants in order to achieve discharge limitations established 

under the Clean Water Act and National Pollution Discharge Elimination System (NPDES) The 

treatment system must be reliable and performance must be continuously achieved throughout all 

seasons of the year. Elements such as chloride, mercury, selenium, and arsenic are generally of 

concern in these wastewaters. Generic parameters such as biochemical oxygen demand (BOD) 

and chemical oxygen demand (COD) may also be targeted constituents for treatment. The 

specific targeted constituents vary spatially throughout the U.S., therefore discharge limits of 

these constituents were chosen to encompass the majority of regulatory NPDES limits. 

Specifically designed constructed wetland treatment systems have been used to treat each of 

these elements independently, and we have recent data indicating success based upon this 

concept or technology for actual FGD wastewater. Wetlands possess unique reactions not 

occurring in other aquatic or terrestrial systems. Constructed wetlands can be poised or buffered 

to ensure that desired reactions (transfers and transformations) affecting the targeted wastewater 

constituents proceed at predictable rates over long periods. In order to develop confidence in the 

ability of a constructed wetland treatment system to treat a specific FGD wastestream, a pilot 

study is needed. A pilot study will provide strong proof-of-concept data and convincing 

information to assist with regulatory permitting of the full-scale facility. Alternatives to 

treatment with a constructed wetland system are not attractive due to high capital costs and 

continuing high costs associated with operation and maintenance. 

The goal of this project was to design constructed wetland treatment systems to effectively and 

consistently treat FGD wastewater in pilot-scale constructed wetland treatment systems. This 

report describes the progress of this pilot study by reporting the performance of each system and 

evaluates treatment effectiveness during all seasons. The pilot study involves a scaled model 

constructed wetland treatment system (i.e., wetland microcosms to decrease uncertainties and 

confirm design features for the proposed full-scale constructed wetland treatment systems). This 

report identifies the project objectives, outlines methods of analyses, and provides results for the 

pilot study. 

Experimental Methods 

Specific objectives of this pilot-scale research are: 

1. Measure performance of a pilot-scale constructed wetland treatment system in 

 terms of decreases in targeted constituents (Hg, Se and As) in the FGD wastewater. 

2. Determine how the observed performance is achieved (both reactions and rates). 
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3. Measure performance in terms of decreased bioavailability of these elements (i.e. 

 toxicity of sediments in constructed wetlands and toxicity of outflow waters from the 

 treatment system). 

Materials and Methods 

System Configuration 

The pilot constructed wetland treatment system (Fig. 1 and 2) was configured at Clemson 

University in Clemson, SC. The system consists of a 6,800-L upstream equalization basin 

followed by three parallel treatment trains. Each treatment train consists of four stages in series 

(from upstream to downstream), including two wetland cells planted with bulrush, a gravel 

manganese oxidation basin, and a final wetland cell planted with cattails. Each treatment stage 

was comprised of a 378-L Rubbermaid utility tank. Overlying water depth and hydrosoil 

depths were 30 cm each in the wetland cells. Total hydraulic retention time (HRT) was four 

days (24 hours per treatment stage). Wastewater was pumped to each treatment train from the 

equalization basin at a constant rate using FMI (Fluid Metering, Inc.) piston pumps (one pump 

per treatment train). Flow through the treatment system trains was by gravity. 

Figure 1. Schematic of the pilot constructed wetland system for evaluating treatment of FGD 

wastewater. 

Pumps 

Equalization Basin

Flow 

A

B

C

Wetland Cell 1 

Wetland Cell 2 

Manganese 

Oxidation Basin Final Wetland Cell 
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Actual FGD Wastewater 

Actual FGD wastewaters were analyzed for the major elemental constituents of concern (Hg, As, 

Se) using ICP-MS and for other water quality parameters such as Cl, SO4

2-, COD, BOD, NPOC 

TSS, and TDS using Standard Methods for the Examination of Water and Wastewater (APHA 

1998). Simulated FGD wastewater was synthesized based on results from these analyses. 

Simulated FGD Wastewater 

The chemical composition of FGD wastewater is site-specific and a treatment system must be 

robust to treat varying concentrations of toxic constituents. Therefore, four simulated FGD 

wastewaters were used, in order to understand the removal rates and extents of each independent 

wastewater resulting from treatment with specifically designed constructed wetlands. These 

wastewaters included acclimation, high, high-intermediate, low-intermediate, and low ionic 

strength simulated FGD wastewater (see Table 1 and 2). 

Acclimation of the pilot constructed wetland system to mercury, selenium, arsenic, and chloride 

was accomplished (Table 1). Following the treatment acclimation period and finalization of a 

list of constituents targeted for removal, FGD wastewater was simulated and introduced to the 

pilot constructed wetland system. Several source materials were mixed with municipal water 

(5,000 L per week) in the upstream equalization basin to provide the targeted FGD wastewater 

constituents (Table 3). 

Formulation of simulated FGD wastewater initially included CaCl2 as a source for chloride, and 

nitric acid was added to neutralize pH. The final formulation differed from the initial 

formulation in that calcium and magnesium chloride salts were used as chloride sources. In 

subsequent formulations of simulated FGD wastewater fly ash was added and dibasic acid 

(DBA) replaced nitric acid. Formulations were consistent after that adjustment. 

Figure 2. Pilot constructed wetland system at Clemson University for treating 

FGD wastewater. 
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For the first phase of this project, sampling was conducted for elemental analysis (Hg, As, and 

Se) of inflow and outflow wastewater. After four weeks of loading, the pilot constructed wetland 

systems were sampled weekly for all water quality parameters listed in Table 3. Water samples 

were collected in 1000-mL Nalgene containers from the equalization basin and outflow from 

each treatment stage. Outflow samples were collected on a time course commensurate with HRT 

(i.e., wetland cell 1 was sampled 24 h after sampling the equalization basin, wetland cell 2 was 

sampled 48 h after sampling the equalization basin, etc.). Aqueous samples of 10-ml were 

immediately preserved with concentrated trace metal grade nitric acid to pH < 2 for metals 

analysis, while the other 990-ml was retained for the remaining analyses and toxicity tests. 

Table 1. Acclimation FGD wastewater loaded into the pilot-scale constructed wetland treatment 

system (listed as weeks 1-4). 

Constituent Week 1 Week 2 Week 3 Week 4 

Mercury 

(Hg(NO3)2·H2O) 

0.027 mg/L 0.054 mg/L 0.070 mg/L 0.136 mg/L 

Selenium (Na2SeO4) 1.0 mg/L 2.0 mg/L 3.7 mg/L 7.5 mg/L 

Chloride (CaCl2) 1,000 mg/L 2,000 mg/L 4,000 mg/L 6,000 mg/L 

Table 2. Classification and targeted concentrations of elements of interest in four simulated FGD 

wastewaters used throughout this phase one DOE study. 

FGD Wastewater Type Treatment 

Period 

Arsenic Mercury Selenium 

High Ionic Strength Weeks 5-10 0.300 mg/L 0.02 mg/L 8.00 mg/L 

High-Intermediate Ionic 

Strength 

Weeks 11-20 0.180 mg/L 0.002 mg/L 4.50 mg/L 

Low-Intermediate Ionic 

Strength 

Weeks 23-24 0.070 mg/L 0.160 mg/L 1.80 mg/L 

Low Ionic Strength Weeks 21-22 0.0025 mg/L 0.001 mg/L 0.060 mg/L 
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Table 3. Targeted constituents and sources for simulated FGD wastewater. 

Constituent Target Inflow Source Target Outflow 

Concentration Concentration1 

Mercury (Hg) 0.02 mg/L Hg(NO3)2·H2O 0.001 mg/L 

Selenium (Se) 7.4 mg/L Na2SeO4 0.4 mg/L 

Arsenic (As) 0.28 mg/L NaAsO2 0.15mg/L 

Chloride (Cl) 4000 mg/L CaCl2

 MgCl2·6H2O 

Sulfate (SO4

-2) 3000 mg/L CaSO4

Boron (B) 20 mg/L Na2B4O5·8H2O 

Chemical Oxygen 100 mg/L Dibasic Acid (DBA) 

Demand 

Total Suspended 1000 mg/L Fly ash 

Solids 

1

 Target concentrations chosen from reviews of local NPDES permits. 

Additional Analyses 

Oxidation-reduction (redox) potential of wetland hydrosoil was monitored monthly by placing 

platinum-tipped electrodes in situ and measuring the electrochemical potential with an Accumet

calomel reference electrode (Faulkner et al., 1989). Dissolved oxygen and pH of inflow and 

outflow wastewater were measured using YSI and Orion® field instruments, respectively. 

Additional constituents and properties (Table 1) including alkalinity, hardness, conductivity, 

chloride and sulfate concentrations, chemical oxygen demand, biological oxygen demand, nonpurgeable organic carbon, and total and suspended solids were determined according to Standard 

Methods for the Examination of Water and Wastewater (APHA 1998). 

Table 4. Analytical methods for parameters monitored weekly from the FGD pilot constructed 

wetland system. 

Parameter Method Method Detection Limit 

Temperature Direct Instrumentation: YSI Model 52 0.5°C 

pH Direct Instrumentation: Orion Model 420A 0.01 

Conductivity Direct Instrumentation: YSI 30 0.1 μS/cm 

Alkalinity Standard Methods: 2320 B 2 mg/L as CaCO3 

Hardness Standard Methods: 2340 C 2 mg/L as CaCO3 

DO1 Direct Instrumentation: YSI Model 52 0.1 mg/L 
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COD2

 Closed reflux colorimetry (HACH - 3 mg/L 

 modified from Standard Methods: 5220D) 

NPOC3 Shimadzu TOC-V CPH Total Organic 4 μg/L 

 Carbon Analyzer 

BOD5

4

 Standard Methods: 5210 B 0.1 mg/L 

TSS5 Standard Methods: 2540 D 0.1 mg/L 

TDS6

 Standard Methods: 2540 C 0.1 mg/L 

Selenium Inductively Coupled Plasma (ICP): EPA 200.7 0.0022 mg/L 

Mercury Inductively Coupled Plasma (ICP): EPA 200.7 0.0001 mg/L 

Chloride HACH Colorimetric Method 8207 25 mg/L 

Sulfate Standard Methods: 4500 E 1 mg/L 

Arsenic ICP: EPA 200.7 0.0013 mg/L 

Boron ICP: EPA 200.7 0.0009 mg/L 

1

 Dissolved Oxygen 

2

 Chemical Oxygen Demand 

3

 Non-purgable Organic Carbon 

4

 Five-day Biological Oxygen Demand 

5

 Total Suspended Solids 

6

 Total Dissolved Solids 

Evaluation of Wetland Plants 

In response to observed stress of wetland vegetation due to chloride levels (target influent 

concentration 6,000 mg/L), the simulated FGD wastewater was decreased to a chloride 

concentration of 4,000 mg/L to ensure the health of aquatic vegetation. 

Results 

Primary Targeted Constituents 

Mercury

High Ionic Strength FGD Wastewater 

During the fifth week of treatment, the total mercury in the equalization basin was 0.0460 mg/L 

and by the final outflow, the total mercury had declined to 0.0003mg/L. The removal of total 

mercury by the pilot constructed wetland system was 98%, with a 91% removal by the outflow 

of the first wetland cell for this treatment. The following week (week 6), the system produced 

similar results, with removal of 64, 84, 94, and 93% at the outflows of the sequential treatment 

cells. At week 7, the total mercury measured in the equalization basin was 0.0019mg/L. There 

was no removal of mercury in the first two cells, however, 35% decrease in mercury content was 

observed in the manganese oxidation basin and 0.0007 mg/L at the final outflow, which achieved 
-15-

a 61% removal. At week 8, total mercury decreased from 0.0154 mg/L (average inflow 

concentration) to 0.0012 mg/L (average final outflow). The next sampling event began in which 

total mercury decreased from 0.0080 mg/L (inflow average) to 0.0010 mg/L (outflow average) 

(Table 5). Performance between the three treatment trains was similar, with total mercury 

removal averaging 91% (Fig. 3). 

High-Intermediate Ionic Strength FGD Wastewater 

Dilution of the simulated FGD wastewater began with the high-intermediate ionic strength FGD 

wastewater (weeks 11 through 20) to achieve a chloride level (~4,000mg/L) compatible to the 

vegetation. Total mercury during this time decreased from an average (all treatment trains) of 

0.0029 mg/L (±0.0004) mg/L in the inflow to 0.0002 mg/L (±0.00005) mg/L in the final outflow, 

or 94% removal (Fig. 5). 

Low-Intermediate Ionic Strength FGD Wastewater 

Analysis of mercury removal by the pilot constructed wetland systems for week 23 indicated an 

average influent mercury concentration of 0.1467 mg/L (±0.0115) (Fig. 6). Final outflow 

concentrations at this sampling event for treatment trains A, B, and C were 0.0072 mg/L, 0.0010 

mg/L, and 0.0069 mg/L, respectively, or an overall removal of 97%. The final week, week 24, 

influent mercury concentrations averaged 0.17 mg/L (±0.0058), while final outflow 

concentrations for trains A, B, and C were 0.0069 mg/L, 0.0071 mg/L, and 0.0080 mg/L, 

respectively (96% removal) (Fig. 7). 

Selenium

High Ionic Strength FGD Wastewater 

Overall, performance of the pilot system treating undiluted simulated FGD wastewater (~6,000 

mg/L chlorides) was approximately 85% removal of total selenium (Fig. 9). Total selenium 

concentrations in the equalization basin averaged 7.7 mg/L, and ranged from 7.1 to 8.5 mg/L for 

weeks 5 through 7 (Table 5). Selenium concentrations in the outflow of wetland cells 1 and 2, 

the manganese oxidation basins, and final wetland cells averaged 7.4 mg/L, 6.8 mg/L, 6.8 mg/L, 

and 6.0 mg/L, respectively (Fig 8). After week 7, wetland cell 2 from both Trains A and B were 

modified by addition of organic matter; train C remained the same as previous weeks. Total 

selenium was then analyzed in the equalization basin and the outflow from wetland cells 1 and 2 

in each train. Total selenium decreased from 6.3 mg/L in the equalization basin to an average of 

3.8 mg/L for the outflow of cell 1 and 1.3 mg/L for the outflow of cell 2 (Fig. 8) in Trains A and 

B. Total selenium in the final outflow was 0.78 mg/L and 0.88 mg/L from Trains A and B, 

respectively, compared to 2.10 mg/L from Train C (Table 5). Treatment trains improved during 

week 9 sampling and total selenium removal reached 87% compared to the previous 84%. 

High-Intermediate Ionic Strength FGD Wastewater 

Before beginning week 11, the simulated FGD wastewater was diluted with 40% municipal 

water reducing the chlorides to 4000 mg/L to allow for plant stability (health). Selenium removal 

averaged 87% between the A and B trains. The average outflow for 10 weeks (week 11 through 
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week 20) was 0.56mg/L. The average outflow selenium concentration for train A was 0.47 

mg/L, approaching the target outflow concentration of 0.4 mg/L. Trains B and C have averaged 

0.64 and 0.68 mg/L, respectively (Fig. 10). 

Low-Intermediate Ionic Strength FGD Wastewater 

Analysis of selenium removal by the pilot constructed wetland system beginning week 23 

indicated an average influent selenium concentration of 1.87 mg/L (±0.06) (Fig. 11). Final 

outflow concentrations for week 23 for treatment trains A, B, and C were 0.20 mg/L, 0.09 mg/L, 

and 0.28 mg/L, respectively, or an overall removal of 90% (Figure 11). For week 24 sampling, 

total selenium influent concentrations averaged 1.8 mg/L (no standard deviation). Outflow 

concentrations of selenium from the manganese oxidation basins (third treatment stage) reached 

the target level of 0.2 mg/L (Fig. 12). Final outflow selenium concentrations increased slightly 

in trains A, B, and C (concentrations: 0.47 mg/L, 0.70 mg/L, and 0.41 mg/L, respectively). 

Arsenic

High Ionic Strength FGD Wastewater 

Total arsenic concentrations in the equalization basin averaged 0.30mg/L, and ranged from 0.27 

mg/L to 0.34 mg/L for weeks 5 through 7 (Table 5). Arsenic concentrations in the outflows of 

wetland cells 1 and 2, the manganese oxidation basin, and the final wetland cells averaged 

0.6433 mg/L, 0.03588 mg/L, 0.0167 mg/L, and 0.0092 mg/L, respectively. Arsenic removal was 

not enhanced to a discernable degree following hydrosoil amendments to Trains A and B. Total 

As in final outflow of week 8 was 0.0870mg/L and 0.0840 mg/L from Trains A and B, 

respectively, compared to 0.0700 mg/L from Trains C (no amendments made to hydrosoil; Table 

4). At the following sampling events, beginning week 10 performance of all treatment trains 

decreased, only removing 45% compared to 70%. Overall, performance of the pilot system 

treating undiluted simulated FGD wastewater was approximately 59% removal of As (week 8 to 

week 10;Figure 13). Average inflow As concentration for these two sampling events was 0.2983 

mg/L compared to 0.1215 mg/L in the final outflow (Figure 13). 

High-Intermediate Ionic Strength FGD Wastewater 

After diluting the simulated FGD wastewater with 40% municipal water, As removal (average of 

treatment Trains A and B) was 49% (Figure 14). The average outflow As concentration from 

weeks 11 to week 20 for these trains was 0.0832 mg/L. The average outflow As concentration 

for Train A was 0.0616 mg/L, below the target outflow concentration of 0.15mg/L. Trains B and 

C averaged 0.0982 and 0.087 mg/L, respectively (Figure 14). 

Low-Intermediate Ionic Strength FGD Wastewater 

Analysis of arsenic removal by the pilot constructed wetland systems for week 23 indicated an 

average influent arsenic concentration of 0.075 mg/L (±0.001) (Figure 15). Final outflow 

concentrations for week 23 sampling event for treatment trains A, B, and C were 0.043 mg/L, 

0.012 mg/L, and 0.029 mg/L, respectively, or an overall removal of 62% (Figure 15). For week 

24 sampling, total arsenic influent concentrations averaged 0.07 mg/L (±0.003). Final outflow 
-17-

arsenic concentrations increased in trains A, B, and C (concentrations: 0.18 mg/L, 0.23 mg/L, 

and 0.11 mg/L, respectively) and is possibly due to binding of arsenic onto particulates (total 

suspended solids) that is detected by total inorganic analysis. 

Other Constituents of Interest 

Simulated FGD wastewater physical and chemical characteristics are presented in Table 5. 

These parameters were analyzed at the following stages or locations in the pilot constructed 

wetland treatment system: 

1. Equalization Basin 

2. Outflow from the first wetland cell of each train (A-1, B-1, C-1) 

3. Outflow from the second wetland cell of each train (A-2, B-2, C-2) 

4. Outflow from the Manganese Oxidation Basin of each train (A-3, B-3, C-3) 

5. Outflow from final wetland cell of each train (A-4, B-4, C-4) 

pH, Alkalinity, and Hardness

In the equalization basin, pH, alkalinity, and hardness averaged 6.55 (n=2), 22 mg/L as CaCO3 

(n=2), and 4200 mg/L as CaCO3 (n=2), respectively, for week 5 and week 6 of treatment. 

During the next three weeks of treatment (Weeks 7, 8, and 9) the pH, alkalinity, and hardness 

averaged 7.10 (n=3, sd=0.30), 106.67 mg/L as CaCO3 (n=3, sd=21.39), and 9057 mg/L as 

CaCO3 (n=3, sd=1006.54). For the following ten weeks of treatment (Weeks 11 through 20) 

during which the simulated FGD wastewater was diluted, pH averaged 7.00 (n=10, sd=0.26), 

alkalinity averaged 103.40 mg/L as CaCO3 (n=10, sd=10.46), and hardness averaged 6540 mg/L 

as CaCO3 (n=10, sd=2480.23). For the treatment of weeks 22 and 23, pH averaged 6.47, 

alkalinity averaged 115 mg/L as CaCO3 and hardness averaged 7200 mg/L as CaCO3. For the 

last two treatment weeks, weeks 23 and 24, FGD wastewater was had an average pH 6.72, 

average alkalinity of 63 mg/L as CaCO3, and average hardness of 9800 mg/L as CaCO3. 

In the first cell of the treatment system, pH, alkalinity, and hardness averaged 6.44 (n=6, 

sd=0.33), 22.33 mg/L as CaCO3 (n=6, sd=3.44), and 3850 mg/L as CaCO3 (n=6, sd=467.97), 

respectively, for weeks 5 and 6. During the next three weeks of treatment (week 7 through week 

9) the pH, alkalinity, and hardness averaged 7.32 (n=9, sd=0.17), 94 mg/L as CaCO3 (n=9, 

sd=18.14), and 9022 mg/L as CaCO3 (n=9, sd=603.69). For the following ten weeks of 

treatment (Weeks 11 through 20), during which the simulated FGD wastewater was diluted, pH 

averaged 7.07 (n=30, sd=0.23), alkalinity averaged 87.17 mg/L as CaCO3 (n=30, sd=12.26), and 

hardness averaged 5373.33 mg/L as CaCO3 (n=30, sd=1331.56). For the treatment of weeks 21 

and 22, pH averaged 6.85 (n=6, sd=0.20), alkalinity averaged 112.33 mg/L as CaCO3 (n=6, 

sd=1.97), and hardness averaged 6266.67 mg/L as CaCO3 (n=6, sd=206.56). For the last two 

treatment weeks, week 23 and 24, the FGD wastewater had an average pH 6.79 (n=6, sd=0.06), 

average alkalinity of 69 mg/L as CaCO3 (n=6, sd=5.48), and average hardness of 9800 mg/L as 

CaCO3 (n=6, sd=912.14). 

In the second cell of the treatment system, pH, alkalinity, and hardness averaged 5.94 (n=6, 

sd=0.37), 15.33 mg/L as CaCO3 (n=6, sd=4.84), and 3833 mg/L as CaCO3 (n=6, sd=422.69), 
-18-

respectively, for weeks 5 and 6. During the next three weeks of treatment (Week 7 through 9) 

the pH, alkalinity, and hardness averaged 6.66 (n=9, sd=0.35), 98.22 mg/L as CaCO3 (n=9, 

sd=33.11), and 8356 mg/L as CaCO3 (n=9, sd=811.04). For the following ten weeks of 

treatment (week 11 through week 20), during which the simulated FGD wastewater was diluted, 

pH averaged 7.07 (n=30, sd=0.24), alkalinity averaged 88.93 mg/L as CaCO3 (n=30, sd=17.39), 

and hardness averaged 5240 mg/L as CaCO3 (n=30, sd=1580.39). For the treatment of week 21, 

pH averaged 7.34 (n=3, sd=0.20), alkalinity averaged 113.33 mg/L as CaCO3 (n=3 sd=1.15), and 

hardness averaged 6000 mg/L as CaCO3 (n=3, sd=400). For the last two treatment weeks, weeks 

23 and 24, the FGD wastewater had an average pH 6.56 (n=6, sd=0.18), average alkalinity of 

69.67 mg/L as CaCO3 (n=6, sd=9.24), and average hardness of 10933.33 mg/L as CaCO3 (n=6, 

sd=1377.92). 

In the third cell of the treatment system, pH, alkalinity, and hardness averaged 7.21 (n=6, 

sd=0.19), 55 mg/L as CaCO3 (n=6, sd=10.18), and 3783 mg/L as CaCO3 (n=6, sd=495.65), 

respectively, for week 5 and week 6. During the next three weeks of treatment (week 7 through 

week 9) the pH, alkalinity, and hardness averaged 7.22 (n=9, sd=0.32), 101.33 mg/L as CaCO3 

(n=9, sd=24.82), and 7867 mg/L as CaCO3 (n=9, sd=489.89). For the following ten weeks of 

treatment (week 11 through week 20), during which the simulated FGD wastewater was diluted, 

pH averaged 7.26 (n=30, sd=0.24), alkalinity averaged 90.67 mg/L as CaCO3 (n=30, sd=15.04), 

and hardness averaged 5380 mg/L as CaCO3 (n=30, sd=1238.85). For the treatment of weeks 21 

and 22, FGD wastewaters had a pH averaged 7.03 (n=6, sd=0.28), alkalinity averaged 104.67 

mg/L as CaCO3 (n=6, sd=4.50), and hardness averaged 5933.33 mg/L as CaCO3 (n=6, 

sd=733.94). For the last two treatment weeks, week 23 and 24, FGD wastewaters had an average 

pH 6.78 (n=6, sd=0.18), average alkalinity of 76.33 mg/L as CaCO3 (n=6, sd=2.94), and average 

hardness of 11066.67 mg/L as CaCO3 (n=6, sd=1671.73). 

In the fourth cell of the treatment system, pH, alkalinity, and hardness averaged 6.77 (n=6, 

sd=0.09), 56.33 mg/L as CaCO3 (n=6, sd=14.39), and 3616.67 mg/L as CaCO3 (n=6, sd=604.70), 

respectively, for weeks 5 and 6. During the next three weeks of treatment (week 7 through week 

9) the pH, alkalinity, and hardness averaged 7.27 (n=9, sd=0.26), 93.56 mg/L as CaCO3 (n=9, 

sd=22.36), and 7244.44 mg/L as CaCO3 (n=9, sd=904.31). For the following ten weeks of 

treatment (week 11 through week 20), during which the simulated FGD wastewater was diluted, 

pH averaged 7.24 (n=30, sd=0.27), alkalinity averaged 86.80 mg/L as CaCO3 (n=30, sd=15.07), 

and hardness averaged 5846.67 mg/L as CaCO3 (n=30, sd=1560.45). For the treatment weeks 21 

and 22, FGD wastewaters had a pH averaged 7.06 (n=6, sd=0.26), alkalinity averaged 110.33 

mg/L as CaCO3 (n=6, sd=3.44), and hardness averaged 6000 mg/L as CaCO3 (n=6, sd=252.98). 

For the last two treatment weeks, week 23 and week 24, FGD wastewaters had an average pH 

6.82 (n=6, sd=0.11), average alkalinity of 77.67 mg/L as CaCO3 (n=6, sd=5.28), and average 

hardness of 10600 mg/L as CaCO3 (n=6, sd=1356.47). 

Conductivity

Conductivity measurements were 14.98 mS (n=5, sd=0.79) for weeks 5 through 9 in the 

equalization basin. Outflow measurements for conductivity for this time period were 12.58 mS 

(n=15, sd=1.21). For the weeks in which the simulated FGD wastewater was diluted, week 11 

through week 20, the equalization basin averaged 9.21 mS (n=10, sd=0.60) with the outflow 

averaging 9.27 mS (n=30, sd=1.25). For weeks 21 and 22, FGD wastewaters was diluted, with 
-19-

resulting conductivity measurements of 11.06 mS (n=2) in the equalization basin and 10.89 mS 

(n=6, sd=0.58) in the outflow. In the last two weeks of treatment (week 23 and 24), conductivity 

measurements were 11.16 mS (n=2) in the equalization basin and 11.89 mS (n=6, sd=2.27) in the 

outflow. 

NPOC (Non-Purgable Organic Carbon)

In the equalization basin, NPOC averaged 18.47 mg/L (n=2) for weeks 5 and 6. During the next 

three weeks of treatment (week 7 through week 10) NPOC averaged 99.72 (n=3, sd=43.22). For 

the following ten weeks of treatment (week 11 through week 20), during which the simulated 

FGD wastewaters was diluted, NPOC averaged 96.07 mg/L (n=10, sd=52.71). For the treatment 

of week 21 and week 22 NPOC averaged 106.97 mg/L (n=2). For the last two treatment weeks, 

week 23 and week 24, FGD wastewaters had an average NPOC of 161.25 mg/L (n=2). 

In the first cell of the treatment system, NPOC averaged 11.60 mg/L (n=6, sd=1.80) for the first 

two weeks of treatment (week 5 and week 6). During the next three weeks of treatment (week 7 

through week 10) the NPOC averaged 92.49 mg/L (n=9, sd=66.49). For the following ten weeks 

of treatment (week 11 through week 20), during which the simulated FGD wastewater was 

diluted, NPOC averaged 60.58 mg/L (n=30, sd=32.16). For the treatment of 21 and 22, NPOC 

averaged 97.95 mg/L (n=3, sd=34.89). For the last two treatment weeks, week 23 and 24, FGD 

wastewaters had an average NPOC of 61.76 mg/L (n=6, sd=41.25). 

In the second cell of the treatment system, NPOC averaged 9.80 mg/L (n=6, sd=1.59) for the 

first two weeks of treatment (week 5 and week 6). During the next three weeks of treatment 

(week 7 through week 10) the NPOC averaged 75.62 mg/L (n=9, sd=46.59). For the following 

ten weeks of treatment (week 11 through week 20), during which the simulated FGD wastewater 

was diluted, NPOC averaged 53.07 mg/L (n=30, sd=26.68). For the treatment of week 21, 

NPOC averaged 44.28 mg/L (n=3, sd=26.02). For the last two treatment weeks, week 23 and 24, 

FGD wastewaters had an average NPOC of 47.96 mg/L (n=6, sd=7.74). 

In the third cell of the treatment system, NPOC averaged 8.17 mg/L (n=6, sd=2.30) for the first 

two weeks of treatment (week 5 and week 6). During the next three weeks of treatment (week 7 

through week 10) the NPOC averaged 61.21 mg/L (n=9, sd=33.83). For the following ten weeks 

of treatment (week 11 through week 20), during which the simulated FGD wastewater was 

diluted, NPOC averaged 47.42 mg/L (n=30, sd=21.91). For treatment of week 21, NPOC 

averaged 63.11 mg/L (n=3, sd=41.92). For the last two treatment weeks, week 23 and 24, FGD 

wastewaters had an average NPOC of 43.72 mg/L (n=6, sd=16.35). 

In the fourth cell of the treatment system, NPOC averaged 11.52 mg/L (n=6, sd=6.84) for the 

first two weeks of treatment (week 5 and week 6). During the next three weeks of treatment 

(week 7 through week 10) the NPOC averaged 43.99 mg/L (n=9, sd=13.71). For the following 

ten weeks of treatment (week 11 through week 20), during which the simulated FGD wastewater 

was diluted, NPOC averaged 47.27 mg/L (n=30, sd=20.69). For the treatment of week 21, 

NPOC averaged 66.01 mg/L (n=3, sd=14.31). For the last two treatment weeks, week 23 and 24, 

FGD wastewaters had an average NPOC of 38.12 mg/L (n=6, sd=18.97). 
-20-

Solids

Total suspended solids (TSS) was 7.40 mg/L for week 5 and 9.30 mg/L for week 6 in the 

equalization basin. For week 3 (week 7), TSS increased to 1,233 mg/L. Total dissolved solids 

(TDS) was 12,551 mg/L for week 5, 22,996 mg/L for week 6, and 22,080 mg/L for week 7 in the 

equalization basin. For weeks 9 and 10 (prior to diluting simulated FGD wastewater), TSS was 

758 mg/L and 362 mg/L, respectively, and TDS averaged 23,332 mg/L (n=2). For the weeks 11 

through 20, the simulated FGD wastewater was diluted. TSS in the equalization basin averaged 

207 mg/L (n=10, sd=137) and TDS averaged 6,184 (n=10, sd=2967). For weeks 21 and 22, 

FGD wastewaters was diluted, resulting in an average TSS in the equalization basin of 55 mg/L 

(n=2) and an average TDS of 12,534 mg/L (n=2). For the last two weeks of treatment (week 23 

and 24), FGD wastewaters had a TSS and TDS averaged 66.5 mg/L (n=2) and 12,267 mg/L 

(n=2). 

In wetland cell 1, TSS averaged 2.2 mg/L (n=3, sd=0.7) and 12.3 mg/L (n=3, sd=3.7) for week 5 

and week 6 TDS averaged 16,699 mg/L (n=3, sd=1,027) for week 5 and 27,909 mg/L (n=3, 

sd=5,424) for week 6. For week 7, TSS and TDS averaged 9.7 mg/L (n=3, sd=2.0) and 21,672 

mg/L (n=3, sd=1,214), respectively. Prior to diluting simulated FGD wastewater during the 

weeks 9 and 10, TSS averaged 32.3 mg/L (n=6, sd=18.35) and TDS averaged 18,773 mg/L (n=6, 

sd=1315). For the following ten treatment weeks (week 11 through week 20), the simulated 

FGD wastewater was diluted. TSS averaged 68 mg/L (n=27, sd=64.6; for week 19, TSS 

averaged 5,408, n=3, sd=566) and TDS averaged 5,892 mg/L (n=30, sd=2,514). For weeks 21 

and 22, TSS and TDS in wetland cell 1 averaged 55 mg/L (n=6, sd=2.6) and 12,769 mg/L (n=6, 

sd=439), respectively. For week 23 and 24, TSS averaged 83 mg/L (n=6, sd=42) and TDS 

averaged 13,069 mg/L (n=6, sd=5,354). 

In wetland cell 2, TSS averaged 1.2 mg/L (n=3, sd=1.4) and 7.35 mg/L (n=3, sd=2.1) for week 5 

and week 6). TDS averaged 14,023 mg/L (n=3, sd=336) for week 1 and 21,615 mg/L (n=3, 

sd=3,251) for week 2. For the week of 9-15-04, TSS and TDS averaged 11.55 mg/L (n=3, 

sd=2.5) and 19,362 mg/L (n=3, sd=1130), respectively. Prior to diluting simulated FGD 

wastewater during week 9 and week 10, TSS averaged 59 mg/L (n=6, sd=42) and TDS averaged 

20,708 mg/L (n=6, sd=1,552). For the following ten treatment weeks (week 11 through week 

20), the simulated FGD wastewater was diluted. TSS averaged 59 mg/L (n=30, sd=66) and TDS 

averaged 5,770 mg/L (n=30, sd=2,308). For week 21 and week 22, TSS and TDS in wetland cell 

2 averaged 31 mg/L (n=6, sd=12.7) and 9,324 mg/L (n=6, sd=432), respectively. For week 23 

and 24, TSS averaged 81 mg/L (n=6, sd=35) and TDS averaged 12,946 mg/L (n=6, sd=910). 

In wetland cell 3, TSS averaged 2.42 mg/L (n=3, sd=1.0) and 5.93 mg/L (n=3, sd=2.2) for week 

5 and 6. TDS averaged 17,765 mg/L (n=3, sd=1,447) for week 5 and 23,486 mg/L (n=3, 

sd=460) for week 6. For week 7, TSS and TDS averaged 6.45 mg/L (n=3, sd=1.86) and 18,677 

mg/L (n=3, sd=269), respectively. Prior to diluting simulated FGD wastewater during week 9 

and week 10, TSS averaged 34 mg/L (n=6, sd=27) and TDS averaged 19,345 mg/L (n=6, 

sd=779). For the following ten treatment weeks (week 11 through week 20), the simulated FGD 

wastewater was diluted. TSS averaged 59 mg/L (n=30, sd=56) and TDS averaged 5,736 mg/L 

(n=30, sd=3,854). For week 21 and week 22, TSS and TDS in wetland cell 3 averaged 51 mg/L 

(n=6, sd=20) and 12,851 mg/L (n=6, sd=748), respectively. For the weeks of week 23 and 24, 

TSS averaged 104 mg/L (n=6, sd=18) and TDS averaged 13,064 mg/L (n=6, sd=1,197). 
-21-

In wetland cell 4, TSS averaged 0.65 mg/L (n=3, sd=0.71) and 12.22 mg/L (n=3, sd=12.29) for 

week 5 and week 6. TDS averaged 16,180 mg/L (n=3, sd=849) for week 5 and 17,687 mg/L 

(n=3, sd=6,679) for week 6. For week 7, TSS and TDS averaged 6.95 mg/L (n=3, sd=2.8) and 

18,939 mg/L (n=3, sd=624), respectively. Prior to diluting simulated FGD wastewater during 

week 9 and 10, TSS averaged 32 mg/L (n=6, sd=22) and TDS averaged 16,734 mg/L (n=6, 

sd=2,522). For the following ten treatment weeks (week 11 through week 20), the simulated 

FGD wastewater was diluted. TSS averaged 60 mg/L (n=30, sd=71) and TDS averaged 6,061 

mg/L (n=30, sd=2,802). For week 21 and week 22, TSS and TDS in wetland cell 4 averaged 46 

mg/L (n=6, sd=15) and 12,949 mg/L (n=6, sd=893), respectively. For week 23 and 24, TSS 

averaged 103 mg/L (n=6, sd=46) and TDS averaged 12,289 mg/L (n=6, sd=603). 

Chlorides

Chloride concentrations were 5,182 mg/L (n=5, sd=242) for week 5 through week 9 in the 

equalization basin. For weeks 10 through 14, the simulated FGD wastewater was diluted. 

Chlorides in the equalization basin averaged 3,463 mg/L (n=10, sd=464). For week 11 through 

week 20, FGD wastewaters had chloride concentration in the equalization basin of 4,113 mg/L 

(n=2). For the last two weeks of treatment (week 23 and 24), chloride concentration in the 

equalization basin for week 23 was 4,150 mg/L. In wetland cells 1, 2, 3, and 4, chloride 

concentrations were not significantly different from the equalization basin during all treatment 

weeks from week 5 through week 24. 

Sulfate

Sulfate concentrations were 747 mg/L (n=5, sd=373) for the first five treatment weeks (week 5 

through 9) in the equalization basin. For the week 10 through week 14, the simulated FGD 

wastewater was diluted. Sulfates in the equalization basin averaged 854 mg/L (n=10, sd=216). 

For week 11 through week 20, sulfate concentration in the equalization basin of 664 mg/L (n=2). 

For the last two weeks of treatment (week 23 and 24), the average sulfate concentration in the 

equalization basin the last two weeks was 432 mg/L (n=2). In wetland cells 1, 2, 3, and 4, sulfate 

concentrations were not significantly different from the equalization basin during all treatment 

week 5 through week 24. 

Dissolved Oxygen, Biological Oxygen Demand, Chemical Oxygen Demand

In the equalization basin, dissolved oxygen (DO), biological oxygen demand (BOD), and 

chemical oxygen demand (COD) averaged 7.26 mg/L (n=5, sd=1.9), 10.30 mg/L (n=5, sd=4.3), 

and 373 mg/L (n=3, sd=43.4), respectively, for weeks five through week 9. For the following 

ten weeks of treatment (week 11 through week 20), during which the simulated FGD wastewater 

was diluted, DO averaged 7.75 mg/L (n=10, sd=1.56), BOD averaged 14.06 mg/L (n=10, 

sd=5.24), and COD averaged 227 mg/L (n=10, sd=45). For the treatment of week 21 and 22, 

DO averaged 7.95 mg/L and BOD averaged 9.63 mg/L. For the last two treatment weeks, week 

23 and 24, FGD wastewaters had an average DO of 8.48 mg/L, average BOD of 10.48 mg/L, and 

average COD of 239 mg/L. 

In the first wetland cell, DO averaged 8.19 mg/L (n=15, sd=0.95) for week 5 through week 9 

prior to diluting the simulated FGD wastewater. For the treatment of week 5 and week 6, BOD 
-22-

averaged 1.88 (n=6, sd=0.46). For the treatment weeks 7, 9 and 10, BOD averaged 8.41 mg/L 

(n=3, sd=0.11), 12.09 mg/L (n=3, sd=0.58), and 19.83 mg/L (n=3, sd=3.27), respectively. For 

the treatment weeks 7 through 10, COD averaged 329 mg/L (n=9, sd=44). For the treatment 

weeks 11 through 20, the simulated FGD wastewater was diluted, resulting in an average DO of 

8.63 mg/L (n=30, sd=1.3) and average COD of 181 mg/L (n=30, sd=18). BOD averaged 12.65 

mg/L (n=15, sd=5.7) for the weeks 11 through 15, and averaged 3.46 mg/L (n=15, sd=1.52) for 

the weeks16 through 20. For treatment weeks 21 and 22, DO averaged 6.81 mg/L (n=6, 

sd=0.33) and BOD averaged 8.46 mg/L (n=6, sd=1.1). For the last two treatment weeks, (week 

23 and 24). DO averaged 8.73 mg/L (n=6, sd=3.3), BOD averaged 2.92 mg/L (n=6, sd=1.8), and 

COD averaged 257 mg/L (n=6, sd=15). 

In the second wetland cell, DO averaged 7.57 mg/L (n=15, sd=2.2) for weeks 5 through 9 prior 

to diluting the simulated FGD wastewater. For the treatment weeks of, BOD averaged 1.51 

(n=6, sd=0.9). For the treatment weeks 7, 9 and 10, BOD averaged 8.44 mg/L (n=3, sd=0.06), 

6.34 mg/L (n=3, sd=0.92), and 21.32 mg/L (n=3, sd=1.16), respectively. For the treatment 

weeks 7 through 10, COD averaged 278 mg/L (n=9, sd=36). For the treatment weeks 11 through 

20, the simulated FGD wastewater was diluted, resulting in an average DO of 8.69 mg/L (n=30, 

sd=1.1) and average COD of 177 mg/L (n=30, sd=33). BOD averaged 10.49 mg/L (n=15, 

sd=2.9) for the weeks11 through 15, and averaged 3.43 mg/L (n=15, sd=2.1) for the weeks16 

through 20. For the treatment weeks 21 and 22, DO averaged 6.19 mg/L (n=3, sd=0.07) and 

BOD averaged 6.55 mg/L (n=3, sd=0.34). For the last two treatment weeks (weeks 23 and 24), 

DO averaged 8.71 mg/L (n=6, sd=3.3), BOD averaged 4.78 mg/L (n=6, sd=1.7), and COD 

averaged 201 mg/L (n=6, sd=6.7). 

In the third wetland cell, DO averaged 7.36 mg/L (n=15, sd=1.9) for weeks 5 through 9prior to 

diluting the simulated FGD wastewater. For the treatment weeks 5 and 6, BOD averaged 1.17 

(n=6, sd=0.16). For the treatment weeks 7, 9 , and 10, BOD averaged 8.27 mg/L (n=3, sd=0.29), 

7.44 mg/L (n=3, sd=0.5), and 15.46 mg/L (n=3, sd=0.56), respectively. For the treatment weeks 

of7 through 10, COD averaged 253 mg/L (n=9, sd=29). For the treatment weeks of11 through 

20, the simulated FGD wastewater was diluted, resulting in an average DO of 8.84 mg/L (n=30, 

sd=1.4) and average COD of 163 mg/L (n=30, sd=30). BOD averaged 8.37 mg/L (n=15, 

sd=2.66) for the weeks 11 through 15, and averaged 2.25 mg/L (n=15, sd=1.57) for the weeks 

of16 through 20. For the treatment weeks 21 and 22, DO averaged 6.72 mg/L (n=3, sd=0.25) 

and BOD averaged 3.45 mg/L (n=3, sd=1.96). For the last two treatment weeks (23 and 24), DO 

averaged 8.74 mg/L (n=6, sd=3.3), BOD averaged 1.94 mg/L (n=6, sd=0.74), and COD averaged 

197 mg/L (n=6, sd=7). 

In the fourth wetland cell, DO averaged 7.51 mg/L (n=15, sd=1.4) for weeks 5 through 9 prior to 

diluting the simulated FGD wastewater. For the treatment weeks 5 and 6, BOD averaged 0.96 

(n=6, sd=0.26). For the treatment weeks of 7, 9, and 10 BOD averaged 6.30 mg/L (n=3, 

sd=1.27), 6.40 mg/L (n=3, sd=0.14), and 10.76 mg/L (n=3, sd=7.00), respectively. For the 

treatment weeks 7 through 10, COD averaged 202 mg/L (n=9, sd=48). For the treatment weeks 

11 through 20, the simulated FGD wastewater was diluted, resulting in an average DO of 8.74 

mg/L (n=30, sd=1.35) and average COD of 159 mg/L (n=30, sd=48). BOD averaged 4.71 mg/L 

(n=15, sd=2.9) for the weeks 11 through 15, and averaged 1.92 mg/L (n=15, sd=1.35) for the 

weeks 16 through 20. For the treatment weeks 21 and 22, DO averaged 6.73 mg/L (n=3, 
-23-

sd=0.26) and BOD averaged 2.53 mg/L (n=3, sd=1.02). For the last two treatment weeks (week 

23 and week 24) DO averaged 8.72 mg/L (n=6, sd=3.3), BOD averaged 3.18 mg/L (n=6, 

sd=0.95), and COD averaged 184 mg/L (n=6, sd=8.29). 

Hydrosoil Oxidation-Reduction (Redox) Potential

Hydrosoil redox potential from the pilot constructed wetland system is presented in Fig. 13 and 

Table 5. Cells 1 and 2 were designed to be anaerobic, while cells 3 and 4 were designed to be 

essentially aerobic. Redox potential increased during winter months, but remained largely within 

the range of sulfate reduction (approximately –50 to –250 mV) in the anaerobic cells (as 

designed) (Fig. 13). 
 -24-

Table 5. Simulated FGD wastewater physical and chemical properties analyzed in a pilot constructed wetland system

Week 5 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

14.18 7.48 6.21 18 4000 14.82 6.85 ND 7.40 12551 18.41 0.3400 19.4 8.50 

A-1 17.56 6.55 6.09 20 3400 12.99 1.37 ND 1.45 17832 11.83 0.0150 14.4 6.50 

B-1 17.54 6.95 6.20 18 3400 13.49 1.35 ND 2.30 16436 9.72 0.0150 15.5 6.60 C-1 17.08 7.56 6.15 20 3500 13.25 2.03 ND 2.85 15830 9.22 0.0170 15.8 6.90 

A-2 17.51 7.78 5.51 8 3700 12.80 0.80 ND 13788 8.08 ND 11.9 5.50 

B-2 16.45 4.67 5.57 12 3400 13.25 0.52 ND 0.90 13873 8.11 0.0059 13.5 6.30 C-2 16.92 7.16 5.81 18 3300 12.89 0.85 ND 2.70 14408 9.01 0.0076 13.1 6.00 

A-3 14.12 10.53 7.57 60 3300 13.12 1.13 ND 2.05 16668 5.64 0.0190 12.4 5.80 

B-3 12.83 7.44 7.11 68 3400 13.79 1.43 ND 3.60 19405 6.79 0.0052 14.4 6.20 C-3 13.19 8.02 7.26 64 3300 13.46 1.13 ND 1.60 17223 6.27 0.0096 13.4 6.00 

A-4 13.35 7.77 6.70 60 3000 11.76 0.59 ND 1.45 15523 6.18 0.0081 10.5 4.10 

B-4 12.78 7.40 6.65 74 3100 12.58 1.10 ND 0.40 17138 5.93 ND 12.7 5.50 C-4 12.26 8.38 6.84 72 3100 12.20 1.37 ND 0.10 15878 5.60 0.0051 11.9 4.50 

Week 6 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

17.30 9.33 6.89 26 4400 14.46 8.83 ND 9.30 22996 18.52 0.2700 13.2 7.60 

A-1 17.03 9.72 6.86 26 4400 14.93 2.15 ND 14.45 23736 13.70 0.1100 15.5 7.90 

B-1 16.90 9.31 6.69 24 4100 14.82 1.82 ND 8.00 34040 13.18 0.0560 15.6 7.80 C-1 16.40 9.70 6.63 26 4300 14.83 2.55 ND 14.45 25952 11.96 0.0970 16.3 8.20 

A-2 16.86 9.07 6.37 20 4200 14.85 2.72 ND 9.50 23698 11.52 0.0150 16.0 7.80 

B-2 16.60 9.25 6.06 14 4200 14.80 2.24 ND 7.30 23278 11.36 0.0086 15.0 7.70 C-2 16.58 9.74 6.31 20 4200 14.96 1.91 ND 5.25 17868 10.71 0.0100 16.2 7.70 
-25-

Table 4 (Continued).

A-3 17.28 9.01 7.22 46 4200 14.99 1.22 ND 7.75 23064 9.18 0.0120 16.1 7.70 

B-3 17.54 7.75 7.01 46 4300 14.93 1.18 ND 3.50 23418 9.54 0.0052 16.7 8.00 C-3 18.00 7.57 7.08 46 4200 14.88 0.92 ND 6.55 23976 11.59 0.0072 15.4 7.70 

A-4 18.90 7.31 6.77 44 4200 14.02 0.96 ND 7.35 23724 13.69 0.0085 15.3 7.10 

B-4 18.85 7.47 6.79 42 4100 14.14 0.94 ND 26.20 18826 15.19 0.0050 15.7 7.40 C-4 19.11 7.69 6.89 46 4200 14.20 0.80 ND 3.10 10512 22.54 0.0100 16.0 7.50 

Week 7 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

20.34 8.47 6.80 88 8000 14.96 7.79 384 1233.00 22080 63.42 0.3000 21.3 7.10 

A-1 20.11 8.64 7.51 90 8400 15.61 8.52 387 9.85 22226 40.19 0.0710 22.1 7.30 

B-1 20.49 8.54 7.06 56 9600 15.67 8.42 321 7.65 22510 24.96 0.0580 23.9 7.50 C-1 20.21 8.41 7.04 82 9600 15.40 8.30 300 11.60 20280 47.92 0.1400 22.9 7.40 

A-2 20.30 8.50 6.75 64 8400 13.69 8.37 324 9.75 19903 40.71 0.0590 18.9 6.00 

B-2 20.21 8.62 6.93 68 8400 13.93 8.50 321 14.45 20120 41.87 0.0610 20.9 6.90 C-2 20.43 8.59 7.00 74 8000 12.79 8.46 264 10.45 18063 47.65 0.1200 19.6 6.50 

A-3 20.15 8.63 7.07 80 8400 13.01 7.94 249 4.35 18893 37.27 0.0280 19.5 6.30 

B-3 20.48 8.60 6.94 80 8400 13.32 8.48 279 7.10 18376 39.22 0.0170 20.1 6.50 C-3 20.65 8.54 7.06 84 8000 12.80 8.39 288 7.90 18761 44.67 0.0470 20.0 6.50 

A-4 19.88 8.69 7.26 84 8000 12.86 6.26 276 10.20 18285 35.84 0.0170 18.7 5.10 

B-4 20.36 8.64 7.02 76 8400 13.33 7.58 237 4.95 19527 35.89 0.0110 19.3 6.10 C-4 20.42 8.60 7.10 82 8000 13.35 5.05 228 5.70 19005 35.40 0.0180 21.8 6.30 

Week 8 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L Se mg/L 

A-1 In 17.62 9.98 7.19 86 10400 15.09 8.04 310 5.80 22065 31.82 6.3000 

B-1 In 17.02 8.85 7.13 90 9200 14.82 7.95 303 8.85 20218 32.74 6.3000 C-1 In 17.34 10.03 7.07 90 9200 15.14 8.83 - 6.65 20280 34.21 6.2000 
-26-

A-1 17.63 10.12 7.17 92 10000 16.44 5.24 264 1.70 22369 24.43 4.4000 

B-1 17.18 10.16 7.09 86 9600 16.33 4.99 250 9.65 22761 25.67 2.2000 C-1 17.42 10.05 7.15 90 9600 16.31 4.92 236 4.65 23086 30.54 4.9000 

A-2 - - - - - - - - - - - 1.3000 

B-2 18.21 8.98 6.98 84 9600 16.71 8.25 252 5.90 23717 26.09 0.9700 C-2 18.70 10.05 7.03 94 9600 16.75 2.94 235 2.30 23580 24.32 1.8000 

Week 9 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

18.13 6.63 7.09 102 10000 16.32 10.44 326 758.30 22902 88.21 0.2700 23.7 8.00 

A-1 In 17.62 8.01 7.30 104 9200 16.18 12.57 366 185.75 22814 86.07 0.3500 23.9 7.60 

B-1 In 17.47 8.12 7.19 92 9200 16.11 12.84 340 71.40 22834 76.36 0.3100 24.4 8.00 C-1 In 17.73 8.37 7.28 90 9200 16.13 12.38 329 49.00 22752 75.99 0.2800 23.9 7.80 

A-1 17.38 8.45 7.28 94 9200 16.38 11.44 300 31.20 23076 62.75 0.2300 24.4 7.30 

B-1 17.25 7.86 7.33 98 9600 16.38 12.27 390 36.40 22322 54.64 0.2600 23.8 4.90 C-1 18.02 8.51 7.34 98 9600 16.38 12.57 383 46.95 23157 63.31 0.2600 24.2 7.50 

A-2 18.22 3.87 6.98 118 9600 16.49 5.82 304 36.40 20800 63.63 0.2300 24.1 2.40 

B-2 17.44 4.15 6.60 72 8400 16.46 7.40 299 48.65 21834 53.31 0.1600 24.0 2.70 C-2 18.44 4.03 6.96 94 9600 16.48 5.80 256 18.75 22759 50.57 0.1500 23.8 4.50 

A-3 18.39 4.23 7.01 102 8000 14.18 7.95 242 81.90 19747 50.55 0.1700 21.0 1.40 

B-3 18.06 4.35 7.02 94 7200 14.25 7.44 230 24.70 19828 46.50 0.1300 21.6 1.30 C-3 18.32 4.07 7.00 88 8400 13.51 6.94 201 47.70 18587 39.50 0.1300 19.7 3.60 

A-4 18.85 4.99 7.12 82 5600 10.48 6.53 133 32.95 14123 37.41 0.0870 14.5 0.78 

B-4 19.21 5.54 7.09 72 6800 10.70 6.43 153 25.05 14990 31.90 0.0840 15.4 0.88 C-4 19.65 4.50 7.04 78 6400 10.92 6.25 147 19.25 14279 34.12 0.0700 16.0 2.10 
-27-

Week 10 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

21.57 4.39 7.40 130 9200 14.32 17.59 410 361.80 23763 147.53 0.3000 - 7.20 

A-1 In 21.20 6.31 7.12 86 8400 14.35 21.32 330 46.20 22093 245.18 0.3000 - 7.60 

B-1 In 22.00 6.40 7.14 84 8800 14.35 17.05 329 50.70 21.318 205.78 0.3000 - 7.80 C-1 In 21.49 7.51 7.06 116 8000 12.60 20.55 313 24.30 19118 203.02 0.2500 - 6.30 

A-1 21.39 7.60 7.42 98 8400 13.37 22.89 282 11.50 20070 178.53 0.3000 - 2.80 

B-1 21.55 7.76 7.50 122 8400 14.12 20.21 309 49.00 22295 189.41 0.5500 - 2.00 C-1 22.14 7.27 7.44 108 8400 13.34 16.38 293 18.80 20488 170.71 0.4700 - 1.90 

A-2 21.52 8.16 7.72 158 8000 13.48 20.38 234 139.30 20005 70.74 0.1100 - 1.40 

B-2 21.82 7.65 7.46 136 7200 13.62 20.96 270 53.70 21065 157.79 0.3300 - 1.60 C-2 22.17 7.22 7.45 100 7600 13.06 22.62 227 55.70 18264 154.28 0.2800 - 1.30 

A-3 21.46 5.80 7.69 158 7600 13.09 14.82 285 15.30 19242 67.58 0.1400 - 1.30 

B-3 21.98 7.69 7.69 114 7600 13.10 15.67 235 27.50 20347 141.59 0.2300 - 1.20 C-3 22.02 8.11 7.54 112 7200 12.59 15.88 269 7.80 18320 84.03 0.1500 - 0.98 

A-4 21.45 8.68 7.50 130 6800 12.49 3.65 215 33.90 18491 56.82 0.1700 - 0.97 

B-4 21.47 8.56 7.67 118 7600 13.17 17.64 234 72.50 19457 67.64 0.2300 - 0.96 C-4 22.17 8.47 7.62 120 7600 12.45 11.00 197 6.70 19063 60.92 0.0880 - 0.86 

Week 11 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

19.33 8.63 7.40 122 10800 10.07 25.03 283 107.60 10745 91.72 0.1900 - 4.70 

A-1 In 19.53 8.33 7.21 102 9200 9.94 25.12 235 18.40 10244 85.81 0.1800 - 4.50 

B-1 In 19.41 8.25 7.08 114 9200 10.13 24.97 265 20.10 10223 149.23 0.1700 - 4.20 C-1 In 19.68 8.27 7.21 108 9600 10.00 25.08 304 41.20 10600 84.39 0.1800 - 4.50 
-28-

A-1 18.52 8.37 7.40 94 7600 9.47 20.43 171 ND 9798 65.69 0.2900 - 1.80 

B-1 18.29 8.92 7.19 106 5600 10.01 21.21 215 10.70 10481 59.27 0.3000 - 1.60 C-1 18.91 8.39 7.31 96 6800 10.33 22.76 231 7.50 10922 58.25 0.2200 - 2.30 

A-2 18.31 9.09 7.54 140 7600 9.60 14.15 221 3.40 9592 42.83 0.0940 - 1.10 

B-2 17.83 8.90 7.42 82 6400 8.15 13.31 186 1.60 8056 36.20 0.1100 - 1.20 C-2 18.52 9.09 7.45 80 5600 8.09 10.96 169 4.10 8186 34.57 0.1500 - 1.10 

A-3 18.55 9.01 7.45 142 7200 9.60 7.02 134 3.20 9784 37.38 0.1100 - 0.77 

B-3 17.71 9.23 7.55 100 6000 9.14 6.87 138 2.00 9412 34.71 0.1300 - 0.74 C-3 18.27 9.18 7.13 88 6800 8.68 6.48 153 8.90 8814 33.51 0.1800 - 0.57 

A-4 19.16 9.14 7.60 120 8800 10.31 2.83 117 1.60 10151 34.20 0.0550 - 0.52 

B-4 18.69 8.53 7.35 90 8000 9.29 1.45 220 0.10 9874 31.14 0.0760 - 0.55 C-4 18.90 8.94 7.43 66 8800 9.08 0.68 150 2.80 9135 31.12 0.1200 - 0.55 

Week 12 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

22.73 7.51 7.41 96 10000 9.51 15.56 279 193.50 10599 177.73 0.1900 - 4.60 

A-1 In 22.20 8.36 7.55 86 9200 9.38 10.67 222 24.20 9639 190.33 0.1800 - 4.50 

B-1 In 21.82 8.38 7.65 86 9200 9.46 13.24 192 24.20 10267 169.85 0.1800 - 4.50 C-1 In 21.89 7.95 7.25 82 9200 9.46 14.84 212 17.90 10805 176.94 0.1600 - 4.30 

A-1 21.89 7.32 7.73 80 8400 8.58 15.40 177 13.50 9173 114.13 0.1700 - 1.10 

B-1 21.75 8.50 7.39 75 8800 9.27 11.29 193 3.90 9083 123.06 0.2000 - 1.90 C-1 21.79 7.78 7.12 78 6400 8.24 14.49 161 4.10 9819 109.50 0.2100 - 1.30 

A-2 21.86 8.33 7.24 116 7600 8.92 14.31 221 54.00 10162 85.04 0.1200 - 0.66 

B-2 22.25 7.56 7.01 112 8800 9.61 10.13 236 6.40 9347 109.21 0.1800 - 0.98 C-2 21.63 8.36 6.78 76 7200 8.60 14.47 205 19.50 9615 94.34 0.2000 - 0.93 

A-3 21.99 8.34 7.56 88 7600 7.69 13.82 221 20.30 8287 77.60 0.0680 - 0.50 

B-3 21.81 8.44 7.30 76 6400 7.78 12.82 287 2.30 7803 71.76 0.1300 - 0.86 C-3 21.44 8.54 7.70 80 6000 7.80 9.10 161 3.60 9197 75.63 0.1300 - 0.64 

A-4 21.46 8.58 7.75 100 7600 8.73 2.07 297 6.60 9169 55.72 0.0270 - 0.25 
-29-

B-4 22.25 8.41 7.36 92 8400 9.33 4.37 224 50.80 10276 72.63 0.1600 - 0.51 C-4 21.36 8.47 7.32 72 7200 8.61 5.27 194 63.40 10132 69.18 0.1700 - 0.57 

Week 13 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

21.17 7.91 7.06 104 9200 8.71 11.68 169 536.00 8894.5 165.64 0.1900 - 4.30 

A-1 In 20.38 7.97 7.09 88 6400 8.65 14.30 210 25.70 8892.5 152.19 0.1600 - 4.10 

B-1 In 21.04 7.87 7.10 98 6800 8.44 11.56 183 30.30 8827.5 143.99 0.1600 - 4.20 C-1 In 20.28 8.00 7.10 80 5600 8.62 12.01 192 21.10 8677 150.40 0.1600 - 4.00 

A-1 20.51 8.01 7.37 62 5200 6.98 6.91 214 4.70 7206.5 97.98 0.1800 - 1.70 

B-1 20.65 8.02 7.28 90 7200 9.04 13.51 174 9.10 8694.5 109.15 0.1900 - 2.10 C-1 20.26 8.01 7.33 60 4800 6.73 1.35 167 4.50 6696.5 51.58 0.1400 - 0.96 

A-2 20.22 8.34 7.35 96 6400 7.94 11.56 234 8.30 8054.5 79.62 0.1400 - 0.83 

B-2 20.28 8.33 7.22 86 8400 8.15 10.89 141 8.60 8423.5 91.34 0.1800 - 1.20 C-2 20.18 8.11 7.14 64 6800 6.70 10.55 221 9.90 6923.5 63.19 0.1800 - 0.75 

A-3 20.65 8.25 7.38 110 7600 8.53 8.28 173 5.50 8542.5 78.34 0.1000 - 0.29 

B-3 20.83 6.80 7.30 116 8000 8.85 9.83 146 2.50 8690.5 80.93 0.1700 - 0.54 C-3 20.09 8.40 7.48 80 6000 6.56 3.88 148 3.20 6903.5 51.31 0.1800 - 0.48 

A-4 21.63 7.92 7.48 114 8800 9.61 4.44 203 2.80 9296.5 63.61 0.0490 - 0.26 

B-4 20.78 7.81 7.49 100 7600 9.24 3.05 100 1.40 9299.5 74.78 0.1300 - 0.51 C-4 21.14 7.51 7.24 86 4400 8.61 4.10 77 14.20 8115.5 59.34 0.0770 - 0.54 

Week 14 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

14.04 11.16 6.99 118 5600 8.68 17.81 169 300.50 3782 142.29 0.1900 - 4.50 

 A-1 In 14.48 12.48 6.97 104 5200 8.61 16.88 210 168.40 4044 125.14 0.1800 - 4.70 

B-1 In 13.48 12.29 6.92 102 5200 8.57 17.18 183 185.30 3680 135.74 0.1800 - 4.70 C-1 In 13.98 11.94 6.95 108 5200 8.60 15.93 192 185.90 4070 126.79 0.1800 - 4.80 
-30-

A-1 13.52 12.36 7.03 104 5200 9.13 10.38 214 225.90 4536 112.44 0.1700 - 3.70 

B-1 12.96 12.30 7.03 106 4800 8.76 12.22 174 184.50 4087 102.06 0.2000 - 3.80 C-1 13.64 12.44 7.01 104 4400 8.12 7.87 167 214.80 4180 77.29 0.1200 - 2.30 

A-2 13.60 11.67 7.13 112 5200 9.03 7.85 234 246.30 4352 86.92 0.0980 - 1.30 

B-2 13.83 11.38 6.93 90 4400 7.86 10.93 141 237.50 4068 94.66 0.0830 - 0.88 C-2 13.55 12.02 7.13 112 4400 8.36 8.28 221 238.00 4947 81.65 0.1500 - 1.40 

A-3 13.77 12.69 7.55 108 5200 9.52 8.93 173 256.80 4984 73.05 0.0880 - 0.64 

B-3 13.34 12.47 7.57 104 5000 8.62 9.83 146 - - 71.37 0.1700 - 1.10 C-3 12.66 12.62 7.08 82 4800 8.36 8.45 148 223.30 4621 72.17 0.0910 - 0.50 

A-4 12.20 12.25 6.85 114 5200 9.77 12.19 203 281.10 4880 65.38 0.1200 - 0.62 

B-4 12.53 12.69 7.26 96 5200 8.68 5.95 100 238.80 4446 71.11 0.1100 - 0.89 C-4 13.30 12.69 7.18 90 5200 8.79 5.59 77 231.20 4512 65.28 0.0660 - 0.47 

Week 15 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L Bmg/L Se mg/

Equal. 

Basin 

23.23 7.25 6.82 92 5200 9.84 15.05 213 148.40 3734.5 117.11 0.2000 - 4.70 

A-1 In 22.92 7.66 6.90 88 5200 9.48 14.37 180 - 3292.5 94.17 0.2000 - 4.70 

B-1 In 22.40 7.62 6.77 92 5200 9.69 13.74 180 55.50 2957.5 89.15 0.1900 - 4.50 C-1 In 22.65 7.76 6.95 88 5200 9.78 15.38 189 43.70 3753.5 86.22 0.2000 - 4.90 

A-1 22.92 7.66 6.90 88 5200 9.48 14.37 180 - 3292.5 94.17 0.2000 - 4.70 

B-1 22.21 7.92 6.83 96 5600 9.98 11.53 165 31.90 3670.5 79.47 0.1900 - 2.50 C-1 22.75 8.08 6.95 94 5600 10.04 11.93 188 38.90 3776.5 67.48 0.1900 - 2.40 

A-2 22.28 8.20 6.95 106 5600 10.30 8.01 173 32.00 4553.5 65.43 0.2400 - 1.10 

B-2 22.07 8.22 6.98 102 5600 10.17 8.00 185 58.20 4252.5 65.74 0.1700 - 1.40 C-2 22.32 8.57 6.85 90 5600 10.40 3.93 179 35.20 3842.5 64.39 0.0880 - 0.73 

A-3 22.07 8.22 6.98 102 5600 10.17 8.00 185 58.20 4252.5 65.74 0.1700 - 1.40 

B-3 22.08 8.35 7.00 102 6000 10.41 8.17 191 57.20 3990.5 66.63 0.2400 - 0.65 C-3 21.65 8.49 7.00 102 6000 10.21 7.67 180 38.30 3855.5 60.75 0.2100 - 0.69 

A-4 22.00 8.54 7.01 112 6200 11.02 3.64 183 47.20 4172.5 56.89 0.0780 - 0.43 

B-4 22.26 8.34 7.04 94 6200 10.80 7.91 165 22.00 4610.5 76.67 0.2300 - 0.88 
-31-

C-4 22.24 8.39 6.86 82 6200 10.75 7.16 195 30.20 4644.5 74.28 0.1000 - 0.51 

Week 16 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

23.25 7.79 6.79 100 6000 9.94 15.82 184 72.20 5797.5 88.14 0.1600 - 3.90 

A-1 In 22.56 8.27 6.83 94 5200 9.97 10.47 179 84.10 5132.5 68.10 0.1600 - 4.20 

B-1 In 22.80 7.28 6.83 92 5200 9.97 6.91 174 110.50 4151.0 66.36 0.1500 - 4.00 C-1 In 21.68 7.62 6.80 90 5200 10.02 5.98 179 96.20 5278.5 56.97 0.1600 - 4.00 

A-1 22.18 8.25 6.87 84 5200 10.32 2.65 174 69.20 6267.5 59.50 0.1700 - 2.80 

B-1 22.01 8.13 6.85 94 5600 10.28 4.01 165 161.60 5873.5 57.55 0.1800 - 2.70 C-1 21.30 8.34 6.87 82 6400 12.25 2.88 183 69.50 6811.5 47.74 0.1100 - 1.20 

A-2 21.81 8.53 6.90 92 6000 10.75 2.10 165 73.30 6488.5 49.55 0.0690 - 0.90 

B-2 22.13 8.33 6.87 88 5600 10.48 1.87 165 62.80 6134.5 49.66 0.1300 - 1.80 C-2 22.70 8.24 6.65 78 4800 11.17 1.16 156 77.00 6403.5 37.87 0.0330 - 0.21 

A-3 22.32 8.33 7.03 100 5600 11.07 1.32 165 53.00 5748.5 46.69 0.0500 - 0.36 

B-3 21.98 8.05 6.90 86 5600 10.45 6.92 165 58.70 5723.5 49.88 0.1000 - 0.51 C-3 22.16 8.42 6.90 78 5600 10.58 4.00 152 70.90 6373.5 44.73 0.1400 - 0.38 

A-4 21.86 8.44 6.92 84 6400 11.74 0.57 170 98.70 6026.5 47.40 0.0280 - 0.37 

B-4 22.22 8.26 6.93 80 5200 11.01 3.72 164 44.60 6530.5 48.75 0.0540 - 0.46 C-4 21.57 8.36 6.88 80 4800 11.77 2.72 194 86.50 6701.5 46.00 0.0410 - 0.43 

Week 17 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

21.24 6.65 7.19 96 4000 9.09 13.78 210 138.05 4965 48.47 0.1700 - 4.00 

A-1 In 21.87 7.67 6.97 84 4400 9.12 7.23 176 112.35 5187 53.97 0.1600 - 4.20 

B-1 In 22.14 6.87 6.95 78 4400 9.11 9.49 169 64.65 5074 56.94 0.1600 - 4.10 C-1 In 20.92 7.40 7.02 86 4800 9.11 6.08 173 84.15 5172 58.46 0.1500 - 4.00 

A-1 21.40 8.34 6.90 76 3600 9.39 3.02 164 80.75 5077 37.85 0.1300 - 3.50 

B-1 22.04 8.27 7.16 92 4800 9.35 2.32 163 77.85 5446 31.94 0.1600 - 3.20 
-32-

C-1 21.02 8.35 7.02 88 4800 9.31 2.01 164 98.65 4915 36.09 0.1300 - 3.20 

A-2 21.08 8.11 6.62 66 3600 7.11 5.83 162 53.95 4088 40.97 0.0700 - 1.20 

B-2 22.06 7.78 6.81 76 3200 6.38 7.35 163 48.85 3840 44.62 0.1200 - 1.60 C-2 21.89 7.83 7.01 68 4000 6.10 7.22 164 56.25 3285 47.04 0.0970 - 1.30 

A-3 22.28 8.26 7.38 76 4000 7.96 1.27 156 56.45 4309 27.89 0.0360 - 0.41 

B-3 21.07 8.34 7.18 86 4000 8.78 1.99 160 79.85 4680 27.70 0.1300 - 0.49 C-3 22.03 8.24 7.17 74 4000 7.82 1.58 159 81.45 3946 29.10 0.1000 - 0.71 

A-4 21.52 8.33 7.25 84 5200 9.36 1.24 165 81.75 4710 28.13 0.0220 - 0.34 

B-4 22.65 8.14 7.37 80 4400 9.53 0.82 160 92.55 5113 26.66 0.0610 - 0.61 C-4 20.91 8.43 7.21 80 4800 9.55 0.53 150 45.55 5017 27.46 0.0490 - 0.56 

Week 18 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

22.71 5.02 6.82 92 4400 9.18 7.42 256 240.90 5660 53.66 0.1200 - 3.80 

A-1 In 23.08 5.80 7.21 82 4400 9.07 8.12 225 68.90 4624 48.91 0.1100 - 3.70 

B-1 In 22.56 6.04 6.80 66 4000 9.02 9.95 236 63.20 4387 50.30 0.1000 - 3.70 C-1 In 23.03 6.52 6.90 70 4400 9.03 12.60 238 66.80 4370 45.44 0.1100 - 3.70 

A-1 22.67 8.00 7.01 70 4000 9.07 4.55 187 62.90 4069 35.28 0.0920 - 3.60 

B-1 22.83 8.10 7.13 74 4000 8.95 1.80 195 48.00 4776 31.36 0.0970 - 2.90 C-1 23.11 7.92 7.15 86 4400 9.15 5.42 201 52.80 5565 33.22 0.1000 - 3.40 

A-2 22.25 8.28 6.99 70 3600 9.14 5.75 166 75.60 5426 30.66 0.0540 - 0.71 

B-2 22.54 8.26 7.01 70 3600 9.17 1.96 176 55.70 5667 31.44 0.1000 - 1.70 C-2 23.15 8.24 6.95 72 4000 9.26 3.64 176 47.70 4221 28.80 0.1100 - 2.40 

A-3 23.04 8.55 7.05 76 4000 9.15 2.31 165 45.80 5222 27.12 0.0190 - 0.27 

B-3 23.61 8.51 6.92 78 4000 9.17 3.29 170 51.10 4575 27.53 0.0390 - 0.52 C-3 24.25 8.61 6.94 76 4000 9.15 3.08 175 153.00 4305 - 0.0940 - 1.50 

A-4 23.14 8.21 6.90 70 4800 7.67 2.30 176 53.00 4214 - 0.0340 - 0.58 

B-4 23.04 7.96 6.98 58 4400 7.07 4.76 172 40.30 4030 - 0.0760 - 0.71 C-4 22.69 8.25 6.96 60 4400 7.60 3.65 165 41.50 4346 - 0.0850 - 0.99 
-33-

Week 19 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

22.01 7.30 6.83 104 5200 8.54 7.01 235 95.85 5670 34.83 0.1600 - 4.10 

A-1 In 21.98 7.93 7.21 96 4800 8.60 5.70 193 108.65 5768 34.60 0.1600 - 4.10 

B-1 In 22.17 7.54 7.43 90 5200 8.53 4.83 189 44.55 5728 44.84 0.1500 - 4.60 C-1 In 22.53 7.32 7.38 88 5200 8.88 5.98 190 - 5756 41.71 0.2100 - 4.50 

A-1 21.64 8.25 7.05 80 4800 8.99 5.96 169 47.66 5029 31.48 0.1400 - 3.70 

B-1 21.38 8.19 6.90 84 4800 8.93 5.62 173 38.45 6059 29.64 0.1500 - 3.50 C-1 22.36 8.02 6.72 80 5200 8.62 5.30 176 29.35 5137 27.05 0.1600 - 3.20 

A-2 21.69 8.36 7.42 82 4000 8.66 2.75 156 39.55 5295 20.11 0.0260 - 0.37 

B-2 21.65 8.11 6.90 84 3600 8.12 3.28 142 27.05 5406 20.89 0.0720 - 1.20 C-2 22.24 7.99 7.32 84 4000 8.71 2.37 150 32.25 5948 26.52 0.1200 - 2.20 

A-3 22.52 7.84 7.63 90 4800 8.47 1.62 156 42.45 5598 19.75 0.0240 - 0.28 

B-3 22.16 8.01 7.36 86 4400 8.66 1.03 150 32.75 5535 23.98 0.0530 - 0.43 C-3 22.12 7.96 7.54 80 5200 9.05 1.47 152 35.75 5400 22.82 0.0690 - 1.40 

A-4 22.96 7.44 7.22 84 4800 9.32 1.02 150 36.25 5876 19.31 0.0120 - 0.26 

B-4 22.50 7.65 7.05 80 4000 8.85 0.74 140 39.35 5817 20.57 0.0280 - 0.44 C-4 20.79 8.29 7.30 78 4800 9.30 0.61 125 51.65 6047 21.69 0.0520 - 1.30 

Week 20 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

22.88 8.23 6.69 110 5000 8.50 11.47 276 237.40 1991 41.09 0.1700 - 4.10 

A-1 In 21.94 8.35 6.71 104 5200 8.29 2.12 219 105.80 1930 28.70 0.1500 - 4.10 

B-1 In 21.14 8.45 6.75 106 4800 8.30 2.54 199 81.00 1593 28.84 0.1700 - 4.40 C-1 In 20.78 8.60 6.80 104 4800 8.46 2.73 205 424.00 1785 29.80 0.1600 - 4.30 

A-1 20.27 8.70 6.72 98 3600 8.62 2.35 176 61.00 1774 23.61 0.2600 - 2.90 

B-1 19.82 8.81 6.92 98 4000 8.94 2.35 168 110.90 2039 20.93 0.0860 - 1.60 C-1 20.10 8.83 6.89 98 4000 8.63 1.70 166 22.40 2022 20.14 0.1500 - 2.40 
-34-

A-2 20.55 8.75 7.06 94 4000 8.60 2.21 125 20.60 2395 25.15 0.0940 - 1.70 

B-2 19.82 8.80 7.35 90 3600 8.73 1.74 138 17.60 2171 22.80 0.0970 - 1.90 C-2 19.95 8.85 7.08 90 4000 8.74 2.21 137 29.87 1837 20.80 0.2200 - 2.40 

A-3 19.97 8.92 7.27 92 3600 8.56 1.50 129 20.20 1809 23.60 0.0430 - 0.47 

B-3 19.70 8.85 7.24 90 4000 8.60 1.50 145 16.66 2049 24.35 0.1200 - 1.30 C-3 20.06 8.80 7.30 90 4400 8.68 0.91 142 16.80 2075 22.38 0.1800 - 1.00 

A-4 20.47 8.72 7.70 86 4400 8.07 2.86 116 74.30 2026 20.25 0.1500 - 1.10 

B-4 20.27 8.77 7.66 86 4800 7.48 1.76 110 13.30 1332 - 0.0870 - 0.83 C-4 20.26 8.79 7.60 86 4400 7.21 1.56 98 20.00 1333 21.39 0.1500 - 0.87 

Week 21 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

24.43 7.58 6.56 120 7600 10.97 9.11 NA 51.05 12449 106.97 0.0025 - 0.06 

A-1 In 23.51 6.46 6.76 122 7600 12.47 12.06 NA 57.15 14844 62.47 0.0051 - 0.07 

B-1 In 23.34 6.34 6.79 120 7200 12.82 11.29 NA 60.25 14726 122.58 0.0025 - 0.09 C-1 In 23.29 6.49 6.77 122 7200 12.79 12.12 NA 55.95 15296 160.48 0.0025 - 0.13 

A-1 23.46 7.53 7.04 116 6400 11.44 9.74 NA 53.25 14905 64.18 0.0200 - 0.12 

B-1 23.25 7.55 7.05 112 6400 11.40 7.19 NA 54.55 15448 95.80 0.0220 - 0.09 C-1 23.52 7.95 7.00 112 6400 11.44 7.06 NA 56.55 14871 133.88 0.0120 - 0.11 

A-2 23.66 8.18 7.16 114 5600 10.19 6.93 NA 45.65 8826 71.82 0.0180 - 0.11 

B-2 24.13 8.30 7.30 112 6400 6.65 6.43 NA 24.35 9556 40.91 0.0150 - 0.08 C-2 24.11 8.29 7.56 114 6000 4.65 6.28 NA 22.95 9590 20.10 0.0410 - 0.64 

A-3 25.55 7.53 7.20 108 6000 11.15 6.75 NA 88.85 11916 110.63 0.0083 - 0.08 

B-3 24.86 7.75 7.22 108 6800 10.19 2.13 NA 39.45 13187 47.31 0.0370 - 0.12 C-3 24.95 7.58 7.40 110 6800 7.28 1.57 NA 32.35 13856 31.39 0.0690 - 0.32 

A-4 24.97 7.61 7.19 112 6400 11.65 4.27 NA 70.25 12241 80.12 0.0640 - 0.14 

B-4 24.89 7.73 7.31 114 5600 11.33 2.49 NA 46.05 12844 51.51 0.0120 - 0.13 C-4 24.66 7.57 7.35 114 6000 10.44 2.59 NA 51.35 14123 66.39 0.0300 - 0.25 
-35-

Week 22 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

22.65 8.31 6.37 110 6800 11.15 10.15 NA 58.80 12618 NA 0.0025 - 0.06 

A-1 In 22.49 8.24 6.49 114 6400 13.43 13.56 NA 42.00 14923 NA 0.0025 - 0.07 

B-1 In 22.10 8.35 6.48 112 6400 13.80 12.57 NA 35.60 14871 NA 0.0025 - 0.12 C-1 In 21.78 8.12 6.50 114 6000 13.05 13.12 NA 43.70 15534 NA 0.0025 - 0.08 

A-1 21.08 8.07 6.60 112 6400 12.73 8.79 NA 51.90 14108 NA 0.0089 - 0.10 

B-1 20.95 8.31 6.73 112 6000 11.70 8.91 NA 58.90 14987 NA 0.0170 - 0.13 C-1 20.86 8.23 6.68 110 6000 12.22 9.08 NA 53.20 15063 NA 0.0086 - 0.10 

A-2 - - - - - - - - - - - - - - 

B-2 - - - - - - - - - - - - - - C-2 - - - - - - - - - - - - - - 

A-3 20.62 7.96 6.78 100 5600 9.01 4.37 NA 57.20 12019 NA 0.0270 - 0.14 

B-3 21.06 8.04 6.79 102 5200 9.52 3.85 NA 49.00 12967 NA 0.0170 - 0.06 C-3 20.76 8.15 6.79 100 5200 8.76 2.01 NA 41.56 13158 NA 0.0450 - 0.14 

A-4 20.74 8.12 6.85 106 6000 10.86 2.81 NA 49.20 11987 NA 0.0350 - 0.12 

B-4 20.61 7.95 6.91 108 6400 10.06 1.49 NA 32.00 12548 NA 0.0120 - 0.06 C-4 21.81 8.16 6.72 108 6000 10.99 1.53 NA 29.30 13952 NA 0.1500 - 0.05 

Week 23 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

19.93 8.59 6.88 58 12800 9.43 11.03 241 65.05 12536 228.52 0.0730 - 1.80 

A-1 In 19.84 8.66 6.80 58 13000 9.31 2.46 256 82.80 13543 88.81 0.0740 - 1.80 

B-1 In - - 6.79 60 11600 9.39 3.62 232 95.45 13977 57.54 0.0760 - 1.90 C-1 In 19.55 8.58 6.85 58 10800 9.79 1.98 237 93.55 13358 22.34 0.0750 - 1.90 

A-1 19.79 8.73 6.73 78 11600 9.32 2.58 269 75.95 13994 130.49 0.0500 - 1.50 

B-1 19.51 8.72 6.82 72 10000 7.78 1.64 238 61.40 14631 81.86 0.0530 - 0.30 
-36-

C-1 19.90 8.65 6.83 70 12800 9.62 5.63 255 66.30 14392 22.66 0.0600 - 1.70 

A-2 20.64 8.53 6.55 64 11600 10.74 7.21 199 63.75 11495 37.24 0.1600 - 0.58 

B-2 19.84 8.68 6.34 80 9600 9.57 3.87 206 82.80 13853 56.77 0.0580 - 0.20 C-2 20.21 8.65 6.33 54 8800 7.72 4.63 194 109.30 13796 55.65 0.0410 - 0.30 

A-3 19.73 8.85 6.75 80 11600 11.31 2.04 205 123.60 12719 12.53 0.0560 - 0.14 

B-3 19.45 8.95 6.54 80 8400 9.54 1.98 186 116.75 12161 54.67 0.0130 - 0.06 C-3 19.56 8.79 6.60 76 9600 10.13 2.39 193 108.10 13566 54.09 0.0850 - 0.25 

A-4 19.56 8.80 6.83 76 10400 11.08 2.81 179 87.50 12646 ND 0.0430 - 0.20 

B-4 20.14 8.66 6.72 74 8800 8.99 3.14 186 99.85 12554 42.03 0.0120 - 0.09 C-4 19.95 8.80 6.65 70 9200 9.67 3.36 181 64.25 13058 57.11 0.0290 - 0.28 

Week 24 Temp C DO mg/L pH Alk mg/L Hard mg/L Cond mS BOD mg/L COD mg/L TSS mg/L TDS mg/L NPOC mg/L As mg/L B mg/L Se mg/

Equal. 

Basin 

20.13 8.37 6.55 68 12400 12.88 9.92 236 67.75 11998 93.98 0.0710 - 1.80 

A-1 In 19.56 8.52 6.59 66 12400 13.14 0.84 233 80.35 12178 44.79 0.0690 - 1.80 

B-1 In 20.25 8.57 6.68 64 12000 13.13 4.40 229 122.35 12770 62.81 0.0730 - 1.80 C-1 In 20.65 8.46 6.71 64 12400 13.06 2.44 245 136.65 11818 55.88 0.0680 - 1.80 

A-1 19.76 8.79 6.69 66 12000 12.34 3.24 275 65.75 8562 

2 

4.46 

0.0820 - 1.30 

B-1 19.56 8.85 6.79 68 11600 12.78 1.04 241 62.65 13396 41.72 0.0490 - 0.41 C-1 20.84 8.64 6.85 68 11600 13.38 11.12 264 168.85 13436 69.36 0.0640 - 1.60 

A-2 19.37 8.80 6.73 74 12000 12.09 5.32 202 98.05 13182 44.74 0.0400 - 0.21 

B-2 19.62 8.86 6.67 72 12000 12.46 2.04 210 61.65 13058 50.83 0.0570 - 0.34 C-2 19.18 8.76 6.72 74 11600 13.51 5.60 193 72.05 12298 42.52 0.0350 - 0.33 

A-3 20.09 8.71 6.97 74 12400 12.87 0.48 199 88.85 13970 40.42 0.0270 - 0.10 

B-3 19.63 8.45 6.88 74 12400 12.97 2.36 197 77.05 14588 54.68 0.0240 - 0.14 C-3 19.35 8.67 6.91 74 12000 13.84 2.40 204 111.45 11380 45.95 0.0170 - 0.21 

A-4 19.44 8.72 6.89 82 11600 13.93 3.60 193 190.25 11374 43.38 0.1800 - 0.47 

B-4 19.91 8.75 6.87 84 11600 13.67 4.52 193 105.15 11852 45.81 0.2300 - 0.70 C-4 19.72 8.61 6.94 80 12000 14.01 1.64 172 70.05 12252 38.82 0.1100 - 0.41 
 -37-

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

Inflow

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Mercury (mg/L)

Week 1 Week 2 Week 3

Figure 3. Total mercury in simulated FGD wastewater treated by a pilot constructed wetland 

system during the acclimation period (Weeks 1 to 4). 

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

Inflow

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Mercury (mg/L)

Train A Train B Train C

Figure 4. Average total mercury in simulated FGD wastewater treated by a pilot constructed 

wetland system for the high ionic strength FGD wastewater (Weeks 9 and 10). 
-38-

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

Inflow

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Mercury (mg/L)

Train A Train B Train C

Figure 5. Average total mercury in simulated FGD wastewater treated by a pilot constructed 

wetland system for the high-intermediate ionic strength FGD wastewater (Weeks 11 to 20). 

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

Inflow 

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Mercury (mg/L)

Train A Train B Train C

Figure 6. Total mercury in simulated FGD wastewater treated by a pilot constructed wetland 

system for the first week of low-intermediate ionic strength FGD wastewater (Week 23). 
-39-

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

Inflow 

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Mercury (mg/L)

Train A Train B Train C

Figure 7. Total mercury in simulated FGD wastewater treated by a pilot constructed wetland 

system for the second week of low-intermediate ionic strength FGD wastewater (Week 24). 

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

Inflow 

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Selenium (mg/L)

Week 1 Week 2

Week 3 Week 4

Figure 8. Total selenium in simulated FGD wastewater treated by a pilot constructed wetland 

system during the acclimation period (Weeks 1 to 4). 
-40-

0

1

2

3

4

5

6

7

8

9

Inflow

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Selenium (mg/L)

Train A Train B Train C

Figure 9. Average total selenium in simulated FGD wastewater treated by a pilot constructed 

wetland system for the high ionic strength FGD wastewater (Weeks 9 and 10). 

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Inflow

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Selenium (mg/L)

Train A Train B Train C

Figure 10. Average total selenium in simulated FGD wastewater treated by a pilot constructed 

wetland system for the high-intermediate ionic strength FGD wastewater (Weeks 11 to 20). 
-41-

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Inflow

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Selenium (mg/L)

Train A Train B Train C

Figure 11. Total selenium in simulated FGD wastewater treated by a pilot constructed wetland 

system for the first week of low-intermediate ionic strength FGD wastewater (Week 23). 

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Inflow 

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Selenium (mg/L)

Train A Train B Train C

Figure 12. Total selenium in simulated FGD wastewater treated by a pilot constructed wetland 

system for the second week of low-intermediate ionic strength FGD wastewater (Week 24). 
-42-

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Inflow

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Arsenic (mg/L)

Train A Train B Train C

Figure 13. Average total arsenic in simulated FGD wastewater treated by a pilot constructed 

wetland system for the high ionic strength FGD wastewater (Weeks 9 and 10). 

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Inflow

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Arsenic (mg/L)

Train A Train B Train C

Figure 14. Average total arsenic in simulated FGD wastewater treated by a pilot constructed 

wetland system for the high-intermediate ionic strength FGD wastewater (Weeks 11 to 20). 
-43-

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

Inflow 

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Arsenic (mg/L)

Train A Train B Train C

Figure 15. Total arsenic in simulated FGD wastewater treated by a pilot constructed wetland 

system for the first week of low-intermediate ionic strength FGD wastewater (Week 23). 

 

0

0.05

0.1

0.15

0.2

0.25

Inflow 

Outflow Cell 1

Outflow Cell 2

Outflow MOB

Final Outflow Cell 4

Total Arsenic (mg/L)

Train A Train B Train C

Figure 16. Total arsenic in simulated FGD wastewater treated by a pilot constructed wetland 

system for the second week of low-intermediate ionic strength FGD wastewater (Week 24). 
-44-

Train A

-250

-200

-150

-100

-50

0

50

100

150

200

August September October November December January

Eh (mvolts)

Cell 1 Cell 2 Cell 3 Cell 4

Figure 17. Hydrosoil oxidation-reduction (redox) potential for Train A of the FGD pilot-scale 

constructed wetland system. 

 

Train B

-200

-150

-100

-50

0

50

100

150

200

August September October November December January

Eh (mvolts)

Cell 1 Cell 2 Cell 3 Cell 4

Figure 18. Hydrosoil oxidation-reduction (redox) potential for Train B of the FGD pilot-scale 

constructed wetland system. 
-45-

Train C

-250

-200

-150

-100

-50

0

50

100

150

August September October November December January

Eh (mvolts)

Cell 1 Cell 2 Cell 3 Cell 4

Figure 19. Hydrosoil oxidation-reduction (redox) potential for Train C of the FGD pilot-scale 

constructed wetland system. 

Table 6. Hydrosoil oxidation-reduction (redox) potential in the FGD pilot constructed wetland 

system. Each redox value represents a mean of two measurements. 

 

 Redox Potential (mV) Redox Potential (mV) 

 

Treatment 

Week 

Cell A 

Train 

B Train C 

Train 

Treatment 

Week 

Cell A Train B Train C Train 

1 - 4 1 -105 -80 -83 14 - 17 1 -46 -26 -25 

 2 -61 -70 -45 2 -120 -81 -107 

 3 13 56 51 3 117 115 117 

 4 84 70 65 4 138 134 127 

5 - 9 1 -125 -144 -121 18 - 22 1 -3 11 -148 

 2 -126 -117 -142 2 1 -98 -55 

 3 28 35 43 3 -89 28 9 

 4 89 70 85 4 58 57 102 

 10 - 13 1 -115 -138 -91 23 - 24 1 -113 -9 -182 

 2 -205 -158 -222 2 -112 -71 -68 

 3 32 5 7 3 -22 90 95 

 4 66 59 100 4 83 144 124 
-46-

Discussion 

Wastewater constituents of primary concern in this study were mercury, arsenic, and selenium. 

These constituents and others were analyzed in the pilot constructed wetland treatment system 

for approximately six months using simulated FGD wastewater. During this time, the effects of 

manipulation and modifications of wetland hydrosoil, hydroperiod, and vegetation were 

evaluated. These manipulations and various initial wastewater conditions have provided 

information for deriving removal rate coefficients necessary for determining adjustments to the 

system to achieve target outflow levels for these constituents. 

 

The initial wetland cells in the series, planted with bulrush and amended with gypsum to provide 

sulfur ligands, effectively decreased the aqueous concentrations of mercury and arsenic dissolved 

in the simulated FGD wastewater. Hydrosoil redox of wetland cells 1 and 2 (A, B, and C) and 

aqueous pH indicated that conditions were favorable for dissimilatory sulfate reduction, which 

provides reduced sulfide for precipitating available cationic metals such as mercury and arsenic 

(Brookins, 1988; Morse, 1995; Carbonell et al., 1999). 

“Redox” is a term used to denote oxidation-reduction. In simple terms, oxidation is loss of 

electrons by a substance and reduction is the gain of electrons. Every oxidation is accompanied 

by a reduction, and vice versa. In wetland hydrosoil, redox may be measured to indicate the 

propensity for certain reactions to occur in that sediment or hydrosoil. Redox potential (Eh) is 

typically measured in hydrosoils and sediments by using platinum electrodes and a portable 

voltmeter. Redox potential is a useful measure of sediment or hydrosoil conditions. In a 

constructed wetland treatment system, multiple measurements of redox potential are required to 

achieve an accurate estimate for this parameter (bulk sediment redox potential) within each cell. 

From site to site within a wetland cell, redox potential can vary widely due to localized 

conditions (e.g. the presence of a root or root hair near an electrode). It is the general redox 

condition within the hydrosoil of the wetland cell that is of interest in order to maintain 

predictable reactions and behaviors of targeted constituents in the hydrosoil. Therefore, the range 

of redox potential measurements is an important functional control parameter for operating 

constructed wetlands treatment systems in a predictable manner. For oxidizing conditions, redox 

potentials greater than –50 mV are appropriate for the desired chemical reactions of this research 

(iron oxyhydroxide precipitates and decreases in COD and BOD). For mildly reducing 

conditions, redox potentials between -50 and –250 mV are the desirable redox ranges for 

elemental immobilization (sorption and precipitation) by reductive chemical pathways. Redox in 

constructed wetlands can be controlled by water depth and sediment amendments or composition 

(sediment oxygen demand). 

Precipitated metal-sulfide minerals are highly insoluble in aqueous systems, which can 

significantly limit the availability of elements to aquatic and terrestrial biota, or in other terms, 

decreasing bioavailability of these elements (Morse, 1995). In anaerobic sediments and wetland 

hydrosoils, mercury is strongly associated (i.e. bond or electrostatic attraction) by the following 

binding mechanisms: (1) sorption on hydrated ferric oxides, (2) surface sorption or ion exchange 

on mineral ion exchangers such as montmorillonite, and (3) sorption and/or chemical binding 

with organic material and sulfur-containing matter. Given an adequate source of sulfide, mercury 

will convert to a stable mercuric sulfide (HgS) with limited availability to aquatic plants and 

animals (Fagerstrom and Jernelov, 1972). 
-47-

The preliminary design of the pilot constructed wetland system included several features for 

selenium removal from FGD wastewater. Not unlike other wastewater constituents, alterations 

in the form of selenium affect solubility and influence mobility, transport, and fate in wetland 

environments. At pH and redox conditions occurring in many aqueous and aerobic sedimentary 

environments, selenium exists as a soluble oxyanion. In strongly reduced environments, selenide 

(Se (-

II)), dominantly exists as H2Se and as insoluble metal selenides (Masscheleyn and Patrick, 

1993). With modifications to wetland cell 2 (addition of organic matter and zero-valent iron), 

enhancement of selenium removal was observed. Under reducing conditions in wetlands, 

elemental selenium and/or metal selenides and selenium-containing sulfur minerals govern 

selenium solubility. Reduction of Se (VI) to Se (IV) and Se (IV) to insoluble Se0

 or Se (-II) is 

expected to occur under the reduced hydrosoil conditions formed by the addition of organic 

matter. The pilot constructed wetland system was designed to provide conditions under which 

insoluble selenium species (e.g., Se0

 or Se (-II)) are likely to form (Masscheleyn et al., 1990; 

Masscheleyn and Patrick, 1993). In addition, zero-valent iron was added to wetland cell 2 and 

the final wetland cell (i.e. cell 4) to complex the residual selenium in the wastewater. 

Chloride levels were not appreciably decreased by the pilot constructed wetland system. 

Chloride is not adsorbed by wetland hydrosoil but is readily transported in aqueous phase 

through the system (Murray-Gulde and Rodgers, 2002). Chloride is taken up by the roots and 

moves upward to accumulate on shoots and leaves; however, these concentrations of chlorides 

within aquatic vegetation do not significantly affect the aqueous concentration as previously 

mentioned. Symptoms for chloride toxicity are leaf “burn” or a drying of leaf tissues. Some 

burn of the shoot and leaf tips was observed in the pilot constructed wetland system, indicating 

that salinity levels in the simulated FGD wastewater were approaching the salinity tolerance 

threshold for these plants. As a result, the simulated wastewater was diluted to 60% with 

municipal water. The wetland vegetation responded positively to the dilution. 

Before the start of the low-intermediate ionic strength FGD wastewater (Week 23), further 

hydrosoil modifications were made and HRT was increased to 30 hours per treatment stage (120 

hours overall). Under these conditions, mercury removal was 96 to 97%, but only achieved the 

target outflow level of 0.001 mg/L in train B during week 23. Selenium removal achieved the 

target level of 0.2 mg/L during the treatment of the low-intermediate ionic strength FGD 

wastewater (weeks 23 and 24). 

Conclusions 

Evaluation of the pilot constructed wetland system clearly indicates that mercury, arsenic, and 

selenium concentrations in FGD wastewater are significantly decreased using this design. Target 

outflow concentrations of mercury and selenium are achievable, as indicated by favorable 

responses in treatment performance following adjustments to the pilot constructed wetland 

system. 
-48-

REFERENCES 

American Public Health Association (APHA), American Water Works Association, and Water 

Pollution Control Federation. 1998. Standard Methods for Examination of Water and 

Wastewater, 20th Ed. American Public Health Association, Washington, D.C. 

Brookins, D.J. 1988. Eh-pH Diagrams for Geochemistry. Springer-Verlag Berlin Heidelberg, 

New York, NY. 

Carbonell, A.A., Porthouse, J.D., Mulbah, C.K., Delaune, R.D., and Patrick, W.H., Jr. 1999. 

Metal solubility in phosphogypsum-amended sediment under controlled pH and redox 

conditions. J. Environ. Qual., 28, 232. 

Fagerstrom, T. and A. Jernelov. 1972. Some aspects of the quantitative ecology of mercury. 

 Water Res. 6: 1193-1202. 

Faulkner, S.P., W.H. Patrick, Jr., R.P. Gambrell. 1989. Field Techniques for Measuring Wetland 

 Soil Parameters. Soil Sci. Soc. Am. J. 53: 883-890. 

Masscheleyn, P.R., R.D. Deluane, and W.H. Patrick, Jr. 1990. Transformations of selenium as 

 affected by sediment oxidation-reduction potential and pH. Environ. Sci. Tech. 24:91-

 96. 

Masscheleyn, P.H. and W.H. Patrick, Jr. 1993. Biogeochemical processes affecting selenium 

 cycling in wetlands. Environ. Tox. Chem.12:2235-2243. 

Morse, J.W. 1995. Dynamics of Trace Metal Interactions with Authigenic Sulfide Minerals in 

 Anoxic Sediments. In Metal Contaminated Aquatic Sediments. H. E. Allen (Ed.), Ann 

 Arbor Press, Inc., Ann Arbor, MI. 

Murray-Gulde, C.L. and J.H. Rodgers, Jr. 2002. Phase II Constructed Wetland Pilot Treatability 

Study On Kern River Produced Water. A Report To: Jim E. Myers, PE, Texaco 

Worldwide E&P, Technology Department, 1111 Bagby, Houston, Texas 77002. 
 -49-

Scientific Final Report 

TASK 2 

Introduction 

The second objective of this research was to determine how the observed performance of 

the pilot scale constructed wetland treatment system was achieved by investigating the 

reactions taking place in the sediments. 

In a constructed wetland treatment system designed to treat constituents of flue gas 

desulfurization (FGD) wastewater, sediment becomes a sink for trace elements such as 

Hg, Se, and As. Determining total concentrations of these constituents in sediment 

cannot provide the required information about mobility, bioavailability, and the potential 

impact on the aquatic system (Michalke, 2003). The distribution of Hg, Se, and As in the 

constructed wetland treatment system depends on their speciation. Speciation defines a 

specific form of an element as to isotopic composition, electronic or oxidation state, or 

molecular structure (MITE, 2003). Speciation can greatly affect the fate and behavior of 

elements in this system, especially of those elements that exist in multiple oxidation 

states, such as Hg, Se, and As. These elements tend to form species differing from those 

of other metals. 

Sequential extraction procedures have been widely used to provide critical information 

on the fate of trace elements in aquatic systems (Tessier et al,. 1979). These procedures 

extract trace elements from sediment with increasing reagent strengths to break down 

sediment matrices and release bound metals into soluble forms with the extractant 

(solvent) used in each step. While this process cannot be used to identify the actual form 

of a given metal in sediment, sequential extractions are useful in categorizing the metals 

into geochemical fractions (McLean and Bledsoe, 1992). Operationally-defined species 

characterization is the characterization of molecule groups (not single species) according 

to their similar behavior during an analytical procedure, such as extraction (Michalke, 

2003). 

Materials and Methods 

Sequential extraction procedures have been developed for mercury (Lechler et al., 1997; 

Wallschläger et al., 1998; Bloom et al., 2003; Beldowski and Pempkowiak, 2003), 

selenium ( Chao and Sanzolone, 1989 and Wang and Chen, 2003), and arsenic (Miller et 

al., 1986; Wenzel et al., 2001; Schank, 2003; Bird et al., 2003), utilizing common 

operationally-defined geochemical fractions to define the distribution of these metals in 

sediment. One fraction extracted is the water-soluble fraction, which contains species 

made up of free ions and ions complexed with soluble organic matter and other 

constituents. Element species in this fraction are the most mobile and potentially the 

most bioavailable species. Another is referred to as the exchangeable fraction, which 

corresponds to the form of elements that can be most readily released into the water 

column. This fraction includes elements that are weakly adsorbed to solid surfaces and 

elements that can be released by ion-exchange processes. Generally, elements in the 
-50-

soluble and exchangeable fractions are considered readily and potentially bioavailable 

(Filgueiras et al., 2002). 

Two additional fractions extracted from sediment are the reducible and oxidizable 

fractions, both of which are relatively stable under normal wetland sediment conditions. 

The reducible fraction includes elements bound to Fe and Mn oxides, which are often 

found in large proportions in sediments. The reduction and dissolution of Fe(III) and 

Mn(IV) will release adsorbed trace elements. The oxidizable fraction includes element 

species that may be associated with various forms of organic matter through 

complexation. The degradation of organic matter, including detritus, under oxidized 

conditions can lead to the release of trace elements bound to this component. These two 

fractions are not considered very mobile or bioavailable (Filgueiras et al., 2002). 

The last fraction utilized in this research is the residual fraction, which includes species 

associated with the crystalline lattice structures of primary minerals and silicates. 

Species in this fraction can only be naturally mobilized as a result of weathering. In 

sequential extraction procedures, this fraction can be mobilized with a very strong acid, 

such as hydrofluoric acid (Filgueiras et al., 2002). 

By categorizing Hg, Se, and As into these geochemical fractions, hypotheses regarding 

reactions occurring in sediment in the constructed wetland treatment system can be 

tested. Furthermore, extractions of these element species are crucial for understanding 

metal biogeochemical behavior in constructed wetlands for FGD wastewater treatment. 

Sequential extraction procedures (as outlined in Tables 7-9) were employed to 

operationally-define the species of Hg, Se, and As in the sediment. Concentrations of 

Hg, Se, and As in sediment fractions were measured according to the standard method 

EPA 200.8 (USEPA, 1994) using a Sciex Elan 9000 Inductively Coupled Plasma- Mass 

Spectrometer (ICP-MS) (Perkin-Elmer, Norwalk, CT). Sediment characteristics including 

pH, redox, cation exchange capacity (CEC), organic matter, solids, and particle size 

distribution were measured. Sediment pH, which is often one of the most important 

factors controlling speciation and equilibria for many contaminants, was measured using 

an YSI pH meter. Redox potential was measured using a digital millivolt meter and 

platinum-tipped electrodes prior to removing sediment samples from the wetland cell to 

avoid false measurements due to sediment disturbance. Particle size distribution analyses 

yielded three fraction sizes: sand, silt, and clay. The hydrometer method was used, as 

described by Gee and Gauder (1986). Percent solids of the sediment were measured 

according to Black (1986). The percent of organic matter in the sediment was measured 

using the lost-on-ignition method, as described by Nelson and Sommers (1996). Cation 

exchange capacity (CEC) of sediment is a measure of the reversibly bound cations in the 

sample. CEC was determined according to methods presented by Plumb (1981). 
-51-

RESULTS 

Table 7. Summary of sequential extraction procedures for Hg (modified from Lechler et 

al. 1997). 

Fraction Description Extraction 

 

1 Elemental (Heating at 180oC) 

2 Exchangeable 0.5 M MgCl2

3 Reducible 0.5 N HCl 

4 Oxidizable 0.3 N NaOH / 4% CH3COOH 

5 Residual (Subtraction from total Hg) 

Table 8. Summary of sequential extraction method for Se (modified from Chao and 

Sanzolone 1989). 

Fraction Description Extraction 

 

1 Soluble; nonspecifically adsorbed 0.25 M KCl 

2 Exchangeable; specifically adsorbed 0.1 M KH2PO4

3 Reducible 4 M HCl 

4 Oxidizable KClO3 and HCl 

5 Residual HNO3

Table 9. Summary of sequential extraction procedure for As (modified from Wenzel et 

al. 2001 and Schank 2003). 

Fraction Description Extractant 

 

1 Soluble; nonspecifically sorbed 0.05 M (NH4)2SO4

2 Exchangeable; specifically sorbed 0.05 M (NH4)2H2PO4

3 Reducible 0.2 M NH4-oxalate buffer; pH 3.25 

4 Oxidizable 0.2 M NH4-oxalate buffer + 0.1 M 

ascorbic acid; pH 3.25 

5 Residual HNO3/aqua regia 

Sediment characteristics, including redox potential, pH, cation exchange capacity (CEC), 

percent organic matter (OM), percent solids, and particle size distribution, are listed in 

Table 9. The redox potentials of sediment in the first and second wetland cells were -410 

mV and -337 mV, respectively. Sediment in the fourth wetland cell had a redox potential 
-52-

of -26 mV. Measurements of sediment pH ranged from 6.63 to 6.80, and the cation 

exchange capacity of sediment ranged from 4.63 me 100g-1 to 6.83 me 100g-1. Percent 

organic matter and percent solids in all sediments ranged from 1.95% to 2.52%, and 

74.67% to 79.14%, respectively. According to the particle size distribution of the 

sediments, a majority of the sediment was sand, with small fractions of clay and silt. 

Results from the sequential extractions of Hg, Se, and As are summarized in Figure 20. 

The total sediment concentrations of Hg, as determined by the summation of individual 

fraction concentrations, were 0.0686 mg/kg, 0.0383 mg/kg, and 0.0282 mg/kg in the first, 

second, and fourth wetland cell, respectively. Mercury is primarily in its elemental 

fraction in the sediment. Unless the sediment is strongly oxidized, mercury in this 

fraction will remain immobile and will not be bioavailable to plants and organisms. Total 

sediment concentrations of Se were 9.353 mg/kg, 19.891 mg/kg, and 16.609 mg/kg in the 

first, second, and fourth wetland cell, respectively. Selenium is distributed amongst 

soluble, exchangeable, reducible, oxidizable, and residual fractions. Selenium is a 

required micronutrient; therefore, these results are not surprising. In a system containing 

large plant densities, selenium is likely to be readily available for plant uptake. Finally, 

total sediment concentrations of As were 25.87 mg/kg, 24.92 mg/kg, and 25.84 mg/kg in 

the first, second, and fourth wetland cell. For the most part, arsenic is not bioavailable to 

plants and organisms, as it resides primarily in the residual fraction. 

Table 10. Summary of sediment characteristics. 

Particle Size Distribution 

Sediment pH Redoxa CECb % OMc % Solids % Sand % Clay % Silt 

 

First wetland cell 6.74 -410 6.83 2.5% 79.1% 91.4% 5.5% 3.0% 

Second wetland cell 6.63 -337 4.63 1.9% 78.8% 91.5% 5.5% 2.9% 

Third wetland cell 6.80 -26 5.08 2.2% 74.6% 89.2% 5.6% 5.1% 

 

 

a

 Redox potential, measured in millivolts 

b

 Cation exchange capacity (me 100g-1) c

 Organic matter 
-53-

Figure 20. Sequential extraction of Hg (A), Se (B), and As (C) in sediment collected 

from the first, second, and fourth planted wetland cells.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1st Wetland Cell 2nd Wetland Cell 4th Wetland Cell

Residual

Oxidizable

Reducible

Exchangeable

Elemental

A

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1st Wetland Cell 2nd Wetland Cell 4th Wetland Cell

Residual

Oxidizable

Reducible

Exchangeable

Soluble

B

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1st Wetland Cell 2nd Wetland Cell 4th Wetland Cell

Residual

Oxidizable

Reducible

Exchangeable

Soluble

C
-54-

Discussion and Conclusions 

Sequential extraction procedures were used as a quantitative measure to evaluate the 

immobilization of these elements of concern in the sedimentary component of these 

systems. Data gathered by this procedure indicate that the majority of As, Hg, and Se are 

bound to residue phases within the sediment, meaning that the dissolution or re-solubility 

of these elements are unlikely to occur under natural environmental conditions set within 

this treatment system (not thermodynamically favored). Mercury was observed to exist in 

two main phases: the residual and elemental, both of which are highly insoluble in the 

aqueous media and relatively stable in terms of transfers and transformations to any other 

phase, except for further transfers into the residual phase. Most selenium existed in 

phases that should not contribute to bioavailability or toxicity, but this will be further 

confirmed with sediment toxicity experiments. Arsenic concentrations were highly 

correlated with the residual phase within these sediments and should not elicit toxicity 

effects due to its binding stability. Data collected from these experiments are utilized 

along with toxicity tests to confirm bioavailability parameters. 
-55-

REFERENCES 

Beldowski, J. and Pempkowiak, J. 2003. Horizontal and vertical variabilities of 

 mercury concentration and speciation in sediments of the Gdansk Basin, Southern 

 Baltic Sea. Chemosphere. 52, 645-654. 

Bird, G., Brewer, P.A., Macklin, M.G., Balteanu, D., Driga, B., Serban, M., and Zaharia, 

 S. 2003. The solid state partitioning of contaminated metals and As in river 

 channel sediments of the mining affecting Tisa drainage basin, northwestern 

 Romania and eastern Hungary. Appl. Geochem. 18, 1583-1595. 

Black, W.C. 1986. Methods of Soil Analysis Part 1. Second Edition, American Society 

 of Agronomy. Madison, WI. 

Bloom, N.S., Preus, E., Katon, J., Hiltner, M. 2003. Selective extractions to assess the 

 biogeochemically relevant fractionation of inorganic mercury in sediments and 

 soils. Anal. Chim. Acta. 479, 233-248. 

Chao, T.T. and Sanzolone, R.F. 1989. Extraction of soil selenium by sequential partial 

 dissolution. Soil Sci. Soc. Am. J. 53, 385-392. 

Filgueiras, A.V., Lavilla, I., and Bendicho, C. 2002. Chemical sequential extraction for 

 metal partitioning in environment solid samples. J. Environ. Monit. 4, 823-857. 

Gee, G.W., and Gauder, J.W. 1986. Particle-Size Analysis. In: Methods of Soil 

 Analysis Part 1. Second Edition, American Society of Agronomy. Madison, WI. 

 383-410. 

Lechler, P.J., Miller, J.R., Hsu, L.C., and Desilets, M.O. 1997. Mercury mobility at the 

 Carson River Superfund Site, west-central Nevada, USA: interpretation of 

 mercury speciation data in mill tailings, soils, and sediments. J. Geochem. 

 Exploration. 58, 259-267. 

McLean, J.E. and Bledsoe, B.E. 1992. Behavior of metals in soil. In: USEPA Office of 

 Research and Development. Ground Water Issue. EPA/540/S-92/018, October 

 1992. 

Metals in the Environment (MITE) Research Network. 2003. Metal sulfide species in 

 surface waters. www.mite-rn.org. 

Michalke, B. 2003. Element speciation definitions, analytical methodology, and some 

 examples. Ecotox. Environ. Safety. 56, 122-139. 

Miller, W.P., Martens, D.C., Zelazny, L.W. 1986. Effect of sequence in extraction of 

 trace metals from soils. Soil Sci. Soc. Am. J. 50, 598-601. 

Nelson, D.W., and Sommers, L.E. 1996. Organic Matter. In: Methods of Soil Analysis 

 Part 3. Soil Science Society of America. Madison, WI. 1004. 

Plumb, R.H., Jr. 1981. Procedures for handling and chemical analysis of sediment and 

 water samples. Technical Report. EPA/CE-18-1. 

Schank, A. 2003. Mobility of arsenic in a shallow aquifer at the Savannah River Site. 

 Masters Thesis, Clemson University. 

Tessier, A., Campbell, P.G.C., and Bisson, M. 1979. Sequential extraction procedure 

 for the speciation of particulate trace metals. Anal. Chem. 51(7): 844-851. 

United States Environmental Protection Agency (USEPA). 1994. EPA Method 200.8, 

 Determination of trace elements in water and wastes by inductively coupled 

 plasma-mass spectrometry, Revision 5.4, Methods for the Determination of 

 Metals in Environmental Samples- Supplement 1, EPA/600/R-94-111. 
-56-

Scientific Final Report 

TASK 3 

Introduction 

For purposes of this research, simulated FGD wastewaters (based on projections from 

actual FGD wastewaters) were used as models for treatment of FGD wastewaters. These 

simulated FGD wastewaters were produced by amending municipal water with arsenic 

(As), mercury (Hg), selenium (Se), chloride (Cl-

) and sulfate (SO4

2-) salts. Three elements 

(As, Hg, and Se) were identified as targeted constituents for this treatment process due to 

their relatively high concentrations in the actual FGD wastewaters, as well as background 

concentrations or pre-existing problems associated with these elements at most power 

company sites. For this research, simulated FGD wastewaters were treated using 

specially designed pilot-scale constructed wetland treatment systems. These systems 

consisted of a detention basin followed by three treatment trains with four wetland 

treatment cells in each train. Discharged wastewater (i.e. outflow wastewater) from the 

full-scale treatment system has to meet water quality criteria set forth under the Clean 

Water Act and the National Pollution Discharge Elimination System (NPDES). Along 

with aqueous concentration limits for selective elements, discharged wastewater must not 

elicit significant toxicity to testing organisms. 

The first objective of this research was to measure changes in concentrations of targeted 

constituents in simulated FGD wastewater before and after treatment by a constructed 

wetland treatment system (untreated inflow versus final outflow of treated FGD 

wastewater). These measurements helped to characterize the potential chemical exposure 

that organisms may encounter if exposed to these wastewaters. Another objective of this 

research was to evaluate the toxicity of aqueous simulated FGD wastewater to 

Ceriodaphnia dubia Richard and Pimephales promelas Rafinesque before and after 

treatment by the pilot-scale constructed wetland treatment system. These two organisms 

are commonly used in the United States for testing waters and wastewaters (U.S. EPA, 

1984). C. dubia is a sentinel invertebrate species widely used for toxicity testing in 

NPDES programs (Spehar and Fiandt, 1986, Mount et al., 1997 Brix et al., 2001). P. 

promelas is a freshwater minnow that is also widely distributed in North America and is 

found in lentic systems. Responses of P. promelas to exposures of metals and organics 

differ from those of C. dubia; therefore both test species were used in this research in 

order to better understand any toxicity of the simulated FGD wastewater (Spehar and 

Fiandt, 1986, USEPA, 1987, Mount et al., 1997). Toxicity endpoints for C. dubia

included mortality and reproduction and for P. promelas endpoints included mortality 

and growth. 

An objective of this research also included toxicity assessment of the sediments within 

the pilot-scale constructed wetland treatment systems. Bulk sediment toxicity testing was 

conducted on previously exposed sediment (hydrosoil) within the constructed wetland 

treatment systems for remediation of simulated FGD wastewaters (Task 1). Two 

commonly used sediment dwelling organisms (Hyalella azteca and Chironomus tentans) 

were used to measure responses of survival and growth after an exposure period of 10 
-57-

days to the treatment hydrosoil. To determine the toxicological significance of these 

results or responses, organisms exposed to sediments from the constructed wetland 

treatment system were compared to controls tested in reference sediment and moderate 

hardness water. 

MATERIALS AND METHODS 

Simulated FGD wastewaters used for this research were modeled after actual FGD 

wastewater projections. Arsenic and mercury were amended using a single reagent salt 

for each element. Selenium, however, was formulated using two reagent salts (sodium 

selenite and sodium selenate) to simulate the speciation of selenium found in actual FGD 

wastewater. All amendments and mixing of the simulated FGD wastewaters were 

conducted in the equalization basin of the system. The species of each element used in 

this research, and the source compound used for amendment of the simulated FGD 

wastewaters are listed in Table 11. 

Sample Collection and Analysis 

Water samples used for analysis (1000-ml) and toxicity testing (4-L) were collected in 

1000-mL Nalgene containers from the equalization basin and final outflow cell from 

the treatment system. Outflow samples were collected on a time course commensurate 

with hydraulic retention time (HRT). Of the 1000-mL water sample collected for 

analysis, a 10-mL aliquot was immediately preserved in the laboratory with concentrated 

trace metal grade nitric acid to pH < 2 for metals analysis, while the remaining volume 

was retained in order to complete the remaining analyses such as chemical oxygen 

demand (COD), pH, alkalinity, hardness, conductivity, and toxicity testing. Methods and 

detection limits for all analyses are listed in Table 12. In order to evaluate variance in 

concentrations of targeted constituents and its effect on toxicity in FGD wastewaters, two 

simulated FGD wastewaters were treated using the constructed wetland treatment system. 

These samples were collected during loading of the low-intermediate ionic strength FGD 

wastewater (treatment weeks 23 and 24), each with inflow (pre-treatment) and outflow 

(post-treatment). However, for clarity purposes throughout the remainder of this report, 

treatment Week 23 and 24 will be denoted as Sample One and Two. 

Table 11. Elements and form used for amendments of simulated FGD wastewater. 

Element Form Compound 

Arsenic As(+III) 100% 

Sodium 

arsenite 

Mercury Hg(+II) 100% 

Mercuric 

nitrate 

Selenium 

Se(+IV) 

33.333% 

Sodium 

selenite 

Selenium 

Se(+VI) 

66.666% 

Sodium 

selenate 
-58-

Table 12. Analytical methods for parameters monitored for FGD wastewater. 

Parameter Method Detection Limit 

Temperature Direct Instrumentation: YSI Model 52 0.5°C 

pH Direct Instrumentation: Orion Model 420A 0.01 

Conductivity Direct Instrumentation: YSI 30 0.1 μS/cm 

Alkalinity Standard Methods: 2320 B 2 mg/L as CaCO3 

Hardness Standard Methods: 2340 C 2 mg/L as CaCO3 

DO1

 Direct Instrumentation: YSI Model 52 0.1 mg/L 

COD2

 Closed reflux colorimetry (HACH - 3 mg/L 

 modified from Standard Methods: 5220D) 

NPOC3

 Shimadzu TOC-V CPH Total Organic 4 μg/L 

 Carbon Analyzer 

BOD5

4

 Standard Methods: 5210 B 0.1 mg/L 

TSS5 Standard Methods: 2540 D 0.1 mg/L 

TDS6

 Standard Methods: 2540 C 0.1 mg/L 

Selenium Inductively Coupled Plasma (ICP): EPA 200.7 0.0022 mg/L 

Mercury Mercury Analyzer: EPA 245.1 0.0001 mg/L 

Chloride HACH Colorimetric Method 8207 25 mg/L 

Sulfate Standard Methods: 4500 E 1 mg/L 

Arsenic ICP: EPA 200.7 0.0013 mg/L 

1

 Dissolved Oxygen 

2

 Chemical Oxygen Demand 

3

 Non-purgable Organic Carbon 

4

 Five-day Biological Oxygen Demand 

5

 Total Suspended Solids 

6

 Total Dissolved Solids 

Constructed Wetland Treatment System 

Specially designed pilot-scale wetland treatment systems were constructed at Clemson 

University in Clemson, SC. The system consisted of a 6,800-L upstream equalization 

basin followed by three parallel treatment trains. The equalization basin was incorporated 

into this treatment process to simulate full-scale design parameters, such as settling of 

particulates and equilibration of elements within the bulk aqueous phase. Each treatment 
-59-

train consisted of four stages in series (from upstream to downstream), including two 

wetland cells planted with Schoenoplectus californicus (C.A. Mey.) Palla (California 

bulrush), a gravel manganese oxidation basin, and a final wetland cell planted with Typha 

angustifolia Linneus (narrowleaf cattail). Each treatment cell consisted of a 378-L 

Rubbermaid utility tank. Overlying water depth and hydrosoil depths were 30 cm each 

in the wetland cells. Total hydraulic retention time (HRT) was four days (24 hours per 

treatment stage). Simulated FGD wastewater was mixed in the equalization basin and 

pumped to each treatment train at a constant flow rate (ml/min) using FMI (Fluid 

Metering, Inc.) piston pumps (one pump per treatment train). Flow of FGD wastewater 

through the treatment system trains was surface flow propagated by gravity, and cells 

were connected by PVC piping. 

 

Toxicity Experiments 

Aqueous Toxicity 

Treatment efficiency of simulated FGD wastewaters by pilot-scale constructed wetland 

treatment systems was accessed by measuring toxicity endpoints for C. dubia and P. 

promelas. Toxicity endpoints for C. dubia included mortality and reproduction, and for P. 

promelas endpoints was mortality. These two organisms are commonly used in the 

United States for testing of waters and wastewaters (Lewis et al., 1994). C. dubia is a 

freshwater microcrustacean, widely distributed in temperate waters throughout North 

America. P. promelas is a freshwater minnow that is also widely distributed in North 

America and is found in lentic systems. For aqueous toxicity assessment, 7-d chronic 

toxicity experiments were conducted with both species using U.S. EPA methods (Lewis 

et al., 1994). Test treatments included an untreated control, as well as inflow and final 

outflow dilutions of simulated FGD wastewater. Dilutions were made using moderate 

hardness laboratory water as defined by Lewis et al. (1994). 

Bulk Sediment Toxicity 

To further understand the chemical fate of As, Hg, and Se in constructed wetland 

treatment systems, evaluation of sediment toxicity was conducted with previously 

exposed hydrosoil used in Task One of this report. Sediment dwelling organisms such as 

Hyalella azteca and Chironomus tentans can provide useful information on the 

bioavailability of toxic elements or molecules when exposed to non-contaminated or 

contaminated sediment. H. azteca and C. tentans have been used in many toxicity 

experiments due to their interaction with freshwater sediments and relative sensitivity to 

contaminants in the sediments (EPA 2000). These experiments along with studies of 

elemental binding strength (Task Two) can be used to further assess the risk posed by 

sediment used in treatment of simulated FGD wastewater with constructed wetland 

treatment systems. For sediment toxicity assessment, 10-d static toxicity experiments 

were conducted with H. azteca and C. tentans following U.S. EPA methods (EPA Test 

Methods 100.1 and 100.2). Test treatments included an untreated control and sediment 

samples from wetland cells 1, 2, and 4. Sediment toxicity experiments were not 

conducted with wetland cell 3, since sediment was not used in the construction of this cell 

(i.e. manganese-oxidation basin). Each experimental treatment included site-sediment 
-60-

volumes of 40 ml and 160 ml of moderately hard water and three replicates. Controls 

were tested in a reference sediment and moderately hard water at the same ratios listed 

above. Survival and growth were measured at the conclusion of the test (10-d). Statistical 

differences were evaluated using chi-square analysis and analysis of variance (ANOVA) 

with least-squared differences (LSD) as the mean separator. H. azteca were supplied food 

in the form of three 7 mm maple leaf discs from initiation to conclusion of the 

experiments. C. tentans were feed 0.5 ml of ground tetramin daily. 

RESULTS 

Removal of Targeted Constituents for FGD Wastewater used in Toxicity Testing 

In order to understand data from toxicity experiments and further characterize simulated 

FGD wastewaters, analyses of parameters such as COD, pH, alkalinity, hardness, 

conductivity, and solids were measured. These data for Sample One and Sample Two 

simulated FGD wastewaters are in Table 12. Results of the first objective, to measure the 

removal of the targeted constituents (As, Hg, Se) from the inflow to the outflow by the 

constructed wetland treatment system, are included in Table 13. 

These data listed in Table 13 indicate that concentrations of arsenic, mercury, and 

selenium decreased from the inflow to final outflow of the treatment system, with the 

exception of arsenic in sample 2, in which the aqueous concentration increased from 

0.071 mg/L to 0.16 mg/L. In this situation, it is assumed that possible particulate 

contamination occurred in the metal analysis aliquot. Another constituent of concern and 

potential source of toxicity, in the simulated FGD wastewater is chlorides. The 

concentration of chlorides decreased from inflow to outflow of treatment system for 

Sample One simulated FGD wastewater. However, in Sample Two simulated FGD 

wastewater, the concentration of chlorides increased from 5250 mg/L to 5416 mg/L. 

Table 13. Water quality parameters of simulated FGD wastewater from inflow to final 

outflow of the pilot-scale constructed wetland treatment systems. 

Parameter Sample 1 Inflow Sample 1 Outflow Sample 2 Inflow Sample 2 Outflow 

Temp °C 19.93 19.88 20.13 19.69 

DO mg/L 8.59 8.75 8.37 8.69 

pH 6.68 6.73 6.55 6.9 

Alk mg/L 58 74 68 82 

Hard mg/L 12800 9400 12400 11700 

Cond mS 9.43 9.91 12.88 13.87 

BOD mg/L 11.03 3.1 9.92 3.25 

COD mg/L 241 182 236 186 

TSS mg/L 65.05 83.87 67.75 121.8 

TDS mg/L 12536 12753 11998 11826 

NPOC mg/L 228.52 33.04 93.98 42.67 

As mg/L 0.073 0.028 0.071 0.17 

Se mg/L 1.8 0.19 1.8 0.52 
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Hg mg/L 0.16 0.005 0.16 0.00733 

Cl-

 mg/L 4150 3800 5250 5416 

SO4 mg/L 407 478 457 625 

Aqueous Toxicity Experiments 

Survival (Inflow to Final Outflow) 

To compare differences in survival from the inflow to final outflow of the treatment 

system using C. dubia and P. promelas, two by two contingency tables (chi squared) 

comparing survival probabilities of inflow vs. outflow dilutions of the simulated FGD 

wastewater were used. Differences were evaluated using Fisher’s exact test (two sided 

probability p =0.05). 

Survival data for Sample One FGD wastewater (Figure 21) indicate that for C. dubia

there was a significant decrease in toxicity from inflow to final outflow of the system for 

the dilutions of 3.125%, 6.25%, 12.5%, and 25% wastewater. Survival data for Sample 

Two (Figure 22) indicate that for C. dubia there was a significant decrease in toxicity 

from inflow to final outflow for the dilutions of 6.25%, 12.5%, and 25% wastewater. For 

P. promelas survival data for the Sample One FGD wastewater (Figure 23) indicate that 

none of the dilutions of wastewater were statistically different from inflow to final 

outflow. Survival data for Sample Two (Figure 24) show that for P. promelas there was a 

significant decrease in toxicity for the dilutions of 6.25% and 12.5% wastewater. 

C. dubia reproductive data (treatments; i.e. dilutions) were evaluated in comparison to 

control organisms using a one-way analysis of variance test (ANOVA; α=0.05) and mean 

separation using a least significant difference test (LSD). For Sample One FGD 

wastewater (Figure 25), there was a significant increase in reproduction from the inflow 

to the outflow of the treatment system for the dilutions of 0.78%, 1.56%, 3.125%, and 

6.25% wastewater. For Sample 2 FGD wastewater (Fig 2.6) there was a significant 

increase in reproduction for the dilutions of 3.125%, 6.25%, and 12.5% wastewater. 

An additional objective of these toxicity experiments was to compare and contrast 

differences in responses of C. dubia and P. promelas to simulated FGD wastewaters. To 

compare differences in survival of C. dubia and P. promelas, a two-by-two contingency 

table (chi-squared) was used to compare the survival probabilities of C. dubia vs. P. 

promelas exposed to varying dilutions of simulated FGD wastewaters. Differences were 

further evaluated using Fisher’s exact test (two sided probability p =0.05). For Sample 

One simulated FGD wastewater (Figure 27), there was a significant difference between 

the responses, in terms of mortality, of C. dubia and P. promelas to wastewater dilutions 

of 3.125%, 6.25%, 12.5%, and 25%. The observed potency (response in organism 

mortality to a change in percentage dilution of wastewater) of Sample One for C. dubia

was 21.32 and 1.2 for P. promelas. For Sample Two (Fig 28) the responses of C. dubia

and P. promelas were significantly different only at a wastewater dilution of 6.25%. The 

observed potency of Sample Two for C. dubia was 4.11 and 7.2 for P. promelas.
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0

20

40

60

80

100

Ctr

0.39

0.781.56

3.125

6.25

12.5

2550

100

Simulated FGD Wastewater (%)

Survival (%)

Pre-treatment Post-treatment

Figure 21. Response, in terms of survival, of C. dubia to the inflow and the outflow from 

the treatment system for Sample One simulated FGD wastewater (Trains A, B, and C 

combined). Concentrations of 0.39% post-treatment and 50% pre-treatment were not 

tested. 

0

10

20

30

40

50

60

70

80

90

100

Ctr 

0.39

0.78

1.56

3.125

6.25

12.5

25

50

100

Simulated FGD Wastewater (%)

Survival (%)

Pre-treatment Post-treatment

Figure 22. Response, in terms of survival, of C. dubia to the inflow and the outflow from 

the treatment system for Sample Two simulated FGD wastewater (Trains A, B, and C 

combined). Concentrations of 0.39% post-treatment and 50% pre-treatment were not 

tested. 
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0

20

40

60

80

100

Ctr

0.39

0.78

1.56

3.125

6.25

12.5

25

50

100

Simulated FGD Wastewater (%)

Survival (%)

Pre-treatment Post-treatment

Figure 23. Response, in terms of survival, of P. promelas to the inflow and the outflow 

from the treatment system for Sample One simulated FGD wastewater (Trains A, B, and 

C combined). Concentrations of 0.39% post-treatment and 50% pre-treatment were not 

tested. 

0

20

40

60

80

100

Ctr 6.25 12.5 25 37.5 50 62.5 75 100

Simulated FGD Wastewater (%)

Survival (%)

Pre-treatment Post-treatment

Figure 24. Response, in terms of survival, of P. promelas to the inflow and the outflow 

from the treatment system for Sample Two simulated FGD wastewater (Trains A, B, and 

C combined). 
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0

5

10

15

20

25

Ctr 

0.39

0.78

1.56

3.125

6.25

12.5

25

50

100

Simulated FGD Wastewater (%)

Reproduction (Mean 

Neonates/Female)

Pre-treatment Post-treatment

Figure 25. Response, in terms of reproduction, of C. dubia to the inflow and the outflow 

from the treatment system for Sample One simulated FGD wastewater (Trains A, B, and 

C combined). Concentrations of 0.39% post-treatment and 50% pre-treatment were not 

tested. 

0

5

10

15

20

25

Ctr

0.39

0.78

1.56

3.125

6.25

12.5

25

50

100

Simulated FGD Wastewater (%)

Reproduction (Mean 

Neonates/female)

Pre-treatment Post-treatment

Figure 26. Response, in terms of reproduction, of C. dubia to the inflow and the outflow 

from the treatment system for Sample Two simulated FGD wastewater (Trains A, B, and 

C combined). Concentrations of 0.39% post-treatment and 50% pre-treatment were not 

tested. 
-65-

Another component of this research was to measure changes in responses of C. dubia and

P. promelas to two temporally separated samples of simulated FGD wastewater each 

possessing different concentrations of constituents. To compare differences in survival of 

C. dubia and P. promelas, a two by two contingency table (chi squared) was used to 

compare survival probabilities of Sample One vs. Sample Two simulated FGD 

wastewater dilutions. Differences were confirmed using Fisher’s exact test (two sided 

probability p =0.05) due to the sample sizes tested (n < 10). 

When comparing C. dubia survival between Sample One and Two FGD wastewaters 

(Figure 29), only the dilutions of 3.125% were statistically different from each other. 

When comparing P. promelas survival between Sample One and Two FGD wastewaters

(Figure 30), only the dilutions of 25% were statistically different, and the dilutions of 

12.5% were close to being statistically different with a p value of 0.0573. Simulated FGD 

wastewaters used in this research were diluted as low as 0.39%, in order to find the no 

observable effect concentration (NOEC) defined in this research as the concentration at 

which reproduction and mortality were not affected (dilutions not statistically different in 

comparison to control organisms for the desired test parameter). Toxicity observed in the 

tested dilutions (both samples) was not solely due to the targeted constituents of concern 

(As, Hg, and Se), but primarily dependent on the chloride concentrations. This statement 

should be reconsidered when chloride concentrations are diluted and do not cause 

significant effects on mortality or reproduction. The NOEC for a chloride-only 

experiment was 640mg/L as Cl-

 (7-day static/renewal toxicity test). With these data, it is 

a fair assumption that toxicity observed at or below 640 mg/L of chlorides is due to 

multiple elements within the matrix tested. Therefore, the pilot-scale constructed wetland 

treatment systems can be classified as performing optimally when NPDES limits and 

toxicity tests are met, but only after dilutions or co-management other mixing waters, 

since chlorides are residual ions in solution that cannot be removed using this treatment 

system. 

The constructed wetland treatment systems used in this research were not designed to 

remove chlorides from the wastewater; and nearly 100% of chlorides input into the 

system remain in solution after discharge from the final wetland cell (variation in 

concentrations occur, i.e. evaporation and precipitation of water). Concentrations of 

chlorides in the undiluted pre-treatment FGD wastewaters and the undiluted posttreatment samples exceeded the known 48-hr LC50 values reported in literature for C. 

dubia and P promelas using MgCl2 and CaCl2. Calcium chloride and magnesium 

chloride are the predominant chlorides found in the FGD wastewater. The 48-hr LC50

values of C. dubia for these two salts reported in literature are 0.88 and 1.83 g/L 

respectively, and 96-hr LC50s were 2.12 and 4.63 g/L respectively for P. promelas 

(Mount et al., 1997). Sample One simulated FGD wastewater had chloride 

concentrations in the pre-treatment and post-treatment that ranged from 3475 mg/L to 

4150 mg/L. For Sample Two simulated FGD wastewater, chloride concentrations ranged 

from 5075 mg/L to 5650 mg/L throughout the test duration from inflow to final outflow. 
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0

20

40

60

80

100

Ctr

0.39

0.78

1.56

3.125

6.25

12.5

25

100

Simulated FGD Wastewater (%)

Survival (%)

C.d. P.p.

Figure 27. Comparative responses, in terms of survival, of C. dubia and P. promelas to 

simulated FGD wastewater Sample One. 

0

20

40

60

80

100

Ctr

0.39

0.78

1.56

3.125

6.25

12.5

25

37.5

50

62.5

75

100

Simulated FGD Wastewater (%)

Survival (%)

C.d. P.p.

Figure 28. Comparative responses, in terms of survival, of C. dubia and P. promelas to 

simulated FGD wastewater Sample Two. Concentrations of 0.39%, 0.78%, 1.56%, and 

3.125% for P. promelas and 37.5%, 50%, 62.5%, and 75% for C. dubia were not tested. 
-67-

Figure 29. Comparative responses, in terms of survival, of C. dubia to simulated FGD 

wastewater Samples One and Two. 

0

20

40

60

80

100

Ctr

0.39

0.78

1.56

3.125

6.25

12.5

25

37.5

50

62.5

75

100

Simulated FGD Wastewater (%)

Survival (%)

Sample 1 Sample 2

Figure 30. Comparative responses, in terms of survival, of P. promelas to simulated 

FGD wastewater Samples One and Two. Concentrations of 0.39%, 0.78%, 1.56%, and 

3.125% for Sample Two (Sample One) and 37.5%, 50%, 62.5%, and 75% for Sample 

One (sample Two) were not tested. 

0

20

40

60

80

100

Ctr 0.39 0.78 1.56 3.125 6.25 12.5 25 100

Simulated FGD Wastewater (%)

Survival (%) Sample 1 Sample 2
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Bulk Sediment Toxicity 

To determine the bioavailability of inorganics (i.e. As, Hg, and Se) in the hydrosoil of the 

constructed wetland treatment system, two sentinel toxicity testing organisms were 

exposed to sediment samples from each wetland cell. Testing organisms were chosen due 

to previous research on sediment toxicity characterization and appropriate EPA methods 

(Lewis et al. 1994; EPA Methods 100.1 and 100.2). 

Hyalella azteca 

In review of results, no observable toxicity effects (survival or growth) were measured 

for sediment samples collected from wetland cells 1, 2, and 4. Complete survival (100%) 

was observed in all treatment and control replicates. Average weight per organism was 

0.00023 g for controls, 0.0006 g for wetland cell 1, 0.0093 g for wetland cell 2, and 

0.00062 g for wetland cell 4. Final weights per organism were greater for treatments in 

comparison to control (Table 13). From these results, there is statistical evidence to 

conclude that survival and growth of H. azteca are impaired by exposure to 

sediments/hydrosoil from constructed wetland treatment systems used in the remediation 

of simulated FGD wastewater. 

Table 14. Sediment toxicity results in terms of survival and growth measurements of 

Hyalella azteca for wetland treatments and controls. 

 

Average 

Percent Total Weight per Average 

Treatment Rep Survival Survival H.a. Wt(g) Org. (g) Wt/Org (g) 

 

 1 10/10 0.00237 0.00024 

 Control 2 10/10 100% 0.00231 0.00023 0.00023 

 3 10/10 0.00211 0.00021 

 1 10/10 0.00339 0.00003 

 1st Wetland Cell 2 10/10 100% 0.00975 0.00010 0.00060 

 3 10/10 0.00488 0.00005 

 1 10/10 0.00296 0.00003 

2nd Wetland Cell 2 10/10 100% 0.0109 0.00011 0.00093 

 3 10/10 0.01409 0.00014 

 1 10/10 0.00841 0.00008 

 4th Wetland Cell 2 10/10 100% 0.00297 0.00003 0.00062 

 3 10/10 0.00711 0.00007 

 

Chironomus tentans 

In review of results, control organisms averaged 90% survival, while the first treatment 

cell averaged 80% survival. Both treatment cells 2 and 4 averaged 96.7% survival. 

Average weight per organism was observed as 0.00089 g for controls, 0.00133 g for 

wetland cell 1, 0.0117 g for wetland cell 2, and 0.00138 g for wetland cell 4. The 

average weight per organism was greater in the three sediment treatments compared to 

the control (Table 14). From these results, there is no statistical evidence to conclude that 

growth of C. tentans is impaired by exposure to sediments/hydrosoil from constructed 

wetland treatment systems used in the remediation of simulated FGD wastewater. 
-69-

Table 15. Sediment toxicity results in terms of survival and growth measurements of 

Chironomus tentans for wetland treatments and controls. 

 

Average 

Percent Total Weight per Average 

Treatment Rep Survival Survival C.t. Wt (g) Org. (g) Wt/Org (g) 

 1 9/10 0.00976 0.00108 

 Control 2 8/10 90% 0.00580 0.00073 0.00089 

 3 10/10 0.00872 0.00087 

 1 10/10 0.00957 0.00096 

 1st Wetland Cell 2 6/10 80% 0.01028 0.00171 0.00133 

 3 8/10 0.01049 0.00131 

 1 10/10 0.01152 0.00115 

 2nd Wetland Cell 2 9/10 96.7% 0.00962 0.00107 0.00117 

 3 10/10 0.01300 0.00130 

 1 10/10 0.01386 0.00139 

 4th Wetland Cell 2 9/10 96.7% 0.01447 0.00161 0.00138 

 3 11/11 0.01272 0.00116 

DISCUSSION 

In the constructed wetland treatment systems, the targeted constituents (As, Hg, and Se) 

decreased from the inflow of the system to the outflow of the system for both samples of 

simulated FGD wastewater. Due to complete mortality of both C. dubia and P. promelas

in both samples of simulated FGD wastewater, dilutions of these samples were used for 

toxicity experiments. Dilutions allowed for determination of upper and lower thresholds 

of toxicity. In the dilutions of simulated FGD wastewater used for toxicity experiments 

both the acute and reproductive toxicity to C. dubia decreased from the inflow to final 

outflow of this treatment system. The pilot-scale wetland treatment system also decreased 

the acute toxicity to P. promelas in dilutions of simulated FGD wastewater from inflow 

to final outflow samples. Understanding that chloride concentrations through the system 

remain relatively unaffected, it can be hypothesized that decreases in toxicity for dilution 

experiments between inflow and outflow samples can be correlated with removal of toxic 

soluble elements (arsenic, mercury, and selenium) by this treatment system. 

Aqueous Toxicity Experiments 

Observed responses of the two species were different as literature suggests (Spehar and 

Fiandt, 1986, USEPA, 1987, Mount et al., 1997), and the observed differences in species 

sensitivity may be attributed to chloride, as the two species respond at different 

concentrations of the two main forms of chloride present. As CaCl2, chloride has a 48-hr 

LC50 of 1.83 g/L for C. dubia and a 96-hr LC50 4.63 g/L for P. promelas. Chloride as 

MgCl2 has a 48-hr LC50 of 0.88 g/L for C. dubia and a 96-hr LC50 of 2.12 g/L for P. 

promelas (Mount et al., 1997) 

When comparing C. dubia survival between treatment weeks (Figure 29) only the 

dilutions of 3.125% were statistically different from each other, in which greater survival 

was observed for Sample One. When comparing P. promelas survival only, the dilutions 
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of 25% were statistically different (Figure 30), and the dilutions of 12.5% were close to 

being statistically different with a p-value of 0.0573. For Sample One, the concentration 

of chlorides was approximately 4150 mg/L while in Sample Two, the concentration of 

chlorides was approximately 5250 mg/L. 

Bulk Sediment Toxicity Experiments 

Hyalella azteca

Toxicity endpoints of survival and growth for H. azteca did not differ significantly 

between sediment treatments (exposed sediment from wetland cells 1, 2, and 4) and 

control organisms. No mortality occurred during the experimental duration of 10-d and 

organism weights were greater for treatment sediments in comparison to controls. In this 

situation, it is plausible to hypothesize that non-toxic food sources (i.e. detritus) were in 

greater abundance than was available in the control sediment. 

Chironomus tentans 

Toxicity endpoints of survival and growth for C. tentans did not differ significantly 

between sediment treatments (exposed sediment from wetland cells 1, 2, and 4) and 

control organisms. Minimal mortality occurred during the experimental duration of 10-d 

and midge weights were greater for treatment sediments in comparison to controls. In this 

situation, it is plausible to hypothesize that non-toxic food sources (i.e. detritus) were in 

greater abundance than in the control sediment. Average survival was observed as 90% 

for controls, 80% for wetland cell 1, and 96.7% for wetland cells 2 and 4.

CONCLUSIONS 

For efficient implementation of FGD scrubber units at fossil-fuel fired power plants, an 

effective and reliable wastewater treatment system is required. Large volumes of FGD 

wastewater will be produced from scrubber systems within smoke stacks, and this 

variable aqueous matrix must be treated to eliminate contaminants in order to achieve 

discharge limitations established under the National Pollution Discharge Elimination 

System (NPDES) and Clean Water Act. Specifically designed constructed wetland 

treatment systems have been used to treat each of these elements independently, (Hansen 

et al., 1998; Kaplan, et al., 2002; Thompson, et al., 2003) but this concept or technology 

had not been “proven” for FGD wastewaters. Wetlands possess unique reactions not 

occurring in other aquatic or terrestrial systems (Jacob and Otte, 2002). This pilot study 

was conducted in order to develop confidence in the ability of a constructed wetland 

treatment system to treat FGD wastewater. 

While the undiluted outflow from this constructed wetland treatment system was toxic in 

terms of reproduction to C. dubia at dilutions as low as 0.78%, this toxicity is likely due 

to the elevated concentration of chlorides (in excess of 4000 mg/L) and not the 

constituents which were targeted for removal by this treatment system. Based on 
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inorganic analysis of pre- and post-treatment wastewater from the pilot-scale constructed 

wetland treatment system, aqueous constituents of concern (As, Hg, and Se) were 

significantly decreased as well as organism responses of toxicity for C. dubia and P. 

promelas. Bulk sediment toxicity, in terms of survival and reproduction, were not 

observed with exposed hydrosoil from any wetland cell treatments and is consistent with 

the sequential extraction data from Task Two. Bioavailability of these elements should 

correlate to estimate binding strengths (sequential extractions). Under this assumption, 

responses of H. azteca and C. tentans indicate that As, Hg, and Se are transferred into 

non-bioavailable forms within the sediment and should not pose a risk unless disturbed. 

Overall, pilot-scale constructed wetland treatment systems decreased aqueous 

concentrations of toxic inorganics and toxic responses of C. dubia and P. promelas with 

co-management of dilution water. These systems can provide scaling coefficients for fullscale design, in which actual FGD wastewater can be treated to meet NPDES restrictions 

of discharge wastewater. 

OVERALL CONCLUSIONS 

Observations from this research indicate that constructed wetland treatment systems 

specially designed for FGD wastewater are both practical and efficient in removal of 

soluble elements of concern (As, Hg, and Se). 

Future research should include continued monitoring of these systems with simulated and 

actual FGD wastewaters for a more comprehensive understanding of temporal variations 

in removal rates and extents of these elements. Also, research should focus on minor 

manipulations of these systems for greater removal of all elements including changes in 

HRTs, organic matter and composition, speciation of iron within selected cells, and 

sulfide concentrations. These data allow a first-order assessment of the chemical 

properties of these precipitated elements within the sediment. 

In conclusion, constructed wetland treatment systems can be utilized for many FGD 

wastewaters. These systems have many advantages in comparison to other treatment 

processes including: public perception (“green” chemistry), low maintenance and simple 

monitoring processes, efficiency in removal rates and extents of elements commonly 

observed in FGD wastewater, minimal capital and operating costs, and spatial 

requirements. 
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